Storage system and data processing system

ABSTRACT

A storage system comprises a data set storage region or storing a data set containing data and update data for managing this data, and a control section. The data set storage region is divided into a plurality of storage regions including a first storage region and a second storage region. The control section generates a first data set containing first data and first update data which is update data for same, stores at least the first data of this first data set in the first storage region, generates a second data set containing second data and second update data which is update data for same, and stores at least the second data of this second data set in the second storage region, which is separate from the first storage region.

CROSS-REFERENCE TO PRIOR APPLICATION

This application relates to and claims priority from Japanese PatentApplication No. 2004-228203, filed on Aug. 4, 2004 the entire disclosureof which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to data storage processing technology, forexample, replication of data between a plurality of storage systems.

BACKGROUND OF THE INVENTION

In recent years, in order to provide continuous service to customers atall times, technology for replicating data between storage systems hasbecome extremely important, in such a manner that a data processingsystem can still provide services even if a problem has occurred in afirst storage system. One example of technology for replicating theinformation stored in the first storage system to a second and a thirdstorage system is that disclosed in the following patent reference.

U.S. Pat. No. 5,170,480 discloses technology whereby a first computerdevice connected to a first storage system transfers the data stored inthe first storage system to a second computer device, via acommunications link between the first computer device and the secondcomputer device, and the second computer device transfers this data to asecond storage system connected to the second computer device.

SUMMARY OF THE INVENTION

The technology disclosed in U.S. Pat. No. 5,170,480 always uses a firstcomputer device and a second computer device in order to replicate data.The first computer device performs normal tasks, and the load on thefirst computer device created by the data replication processing is notinsignificant. Furthermore, there is a problem in that, since acommunications link between the first computer device and the firststorage system is used to transfer the data, the data for replicationmay conflict with data transfer required for normal tasks, therebycausing the data reference time and data update time required for normaltasks to increase.

Moreover, it would also appear to be desirable to improve theperformance of replicating data from the first storage system to thesecond storage system (for example, by shortening the length of timerequired to replicate the data).

Furthermore, if a particular event occurs (for example, if the freestorage space runs out at the destination for the replica data), thenthe process of replicating the data from the first storage system to thesecond storage system may be interrupted, but it would appear to bedesirable to shorten the time period from the time at which the datareplication process is interrupted until the time at which it restarts.

Consequently, it is an object of the present invention to perform datatransfer or data replication between a plurality of storage systems,without affecting the top-level computer device of the storage system.It is a further object of the present invention to avoid affectingcommunications between the storage systems and the computer device.

It is a further object of the present invention to improve theperformance of data replication from a first storage system to a secondstorage system.

It is a yet further object of the present invention to shorten the timeperiod from the interruption of data replication from a first storagesystem to a second storage system, until the restarting of datareplication.

Other objects of the present invention will become apparent from thefollowing description.

The storage system according to a first aspect of the present inventionis a storage system connected to another storage system storing receiveddata; comprising: a data set storage region for storing a data setcontaining data and update data for managing the data; and a controlsection.

The control section generates the data set containing update data formanaging the data, stores the generated data set in the data set storageregion, and sends a data set in the data set storage region to the otherstorage system. The data set storage region is divided into a pluralityof storage regions including a first storage region and a second storageregion. The data comprises first data and second data. In this case, thecontrol section generates a first data set containing the first data andfirst update data, being update data for the first data; stores at leastthe first data of the generated first data set in the first storageregion; generates a second data set containing the second data andsecond update data, being update data for the second data; and stores atleast the second data of the generated second data set in the secondstorage region, being a separate storage region from the first storageregion.

The storage system and the other storage system may respectively be anactual storage device, or they may be systems comprising a plurality ofstorage devices. In the latter case, for example, the first storageregion and the second storage region are respective logical volumes, andthey may be storage regions provided in separate storage devices.

In the first mode of implementing the present invention, each of theplurality of storage regions is divided into an update data sub-regionfor storing the update data of the data set, and a data sub-region forstoring the data of the data set. In this case, the control sectionstores the first data in the data sub-region of the first storageregion, and stores the second data in the data sub-region of the secondstorage region.

In a second mode of implementing the present invention, in the firstmode of implementation, the second data contained in the second data setis data stored subsequently to the first data contained in the firstdata set.

In a third mode of implementing the present invention, the other storagesystem generates a data set read command for reading out the data set,and sends the data set read command thus generated and a regionidentification code for identifying one of the plurality of storageregions, to the storage system. The control section receives the dataset read command and the region identification code from the otherstorage system, reads out update data from the plurality of storageregions in response to the data set read command, further reads out datacorresponding to the update data from the storage region correspondingto the received region identification code, of the plurality of storageregions, and sends the data set comprising the update data and the datathus read out, to the other storage system.

In a fourth mode of implementing the present invention, the storagesystem further comprises: a volume set constituted by one or a pluralityof logical volumes for storing the data sets. The volume set is dividedinto a plurality of sub volume regions. Each of the plurality of storageregions is a sub volume region. Each of the plurality of sub volumeregions extends over one or a plurality of logical volumes.

In a fifth-mode of implementing the present invention, in the fourthmode of implementation, each of the one or plurality of logical volumesis divided into an update data region for storing the update data of thedata sets, and a data region for storing the data of the data sets. Atleast the data region of the update data region and the data region isdivided into a plurality of sub data regions. If there is one of thelogical volumes, then each of the plurality of sub volume regions is asub data region, whereas if there is a plurality of the logical volumes,then each of the plurality of sub volume regions is a sub data regiongroup constituted by a group of a plurality of sub data regionsrespectively provided in the plurality of logical volumes.

In a sixth mode of implementing the present invention, in the fifth modeof implementation, the control section changes the storage destinationfor the data contained in the data set, for each sub volume region.

In a seventh mode of implementing the present invention, in the fourthmode of implementation, the number of the sub volume regions is equal toor greater than the number of the logical volumes.

In an eighth mode of implementing the present invention, the otherstorage system generates a data set read command for reading out thedata set and sends same to the storage system. The control sectionreceives the data set read command from the other storage system, readsout a plurality of data sets from the data set storage region inresponse to the data set read command, and sends same to the otherstorage system.

In a ninth mode of implementing the present invention, in the eighthmode of implementation, the control section reads out a plurality ofdata from consecutive regions of the data set storage region; reads outsa plurality of update data corresponding respectively to the pluralityof data, from the data set storage region; generates the plurality ofdata sets comprising the plurality of data and the plurality of updatedata thus read out, and sends same to the other storage system.

In a tenth mode of implementing the present invention, the storagesystem further comprises a cache memory for temporarily storing datasets exchanged between the other storage system and the data set storageregion. the other storage system generates a data set read command forreading out the data set and sends same to the storage system. In thiscase, the control section receives the data set read command from theother storage system, reads out a data set from the data set storageregion to the cache memory, in response to the data set read command,sends the data set read out to the cache memory to the other storagesystem, reads out a data set from the data set storage region to thecache memory before receiving the next data set read command, and sendsthe data set stored in the cache memory to the other storage system,when the next data set read command is received.

In an eleventh mode of implementing the present invention, the otherstorage system comprises a secondary logical volume. The storage systemfurther comprises: a primary logical volume for storing data, forming apair with the secondary logical volume and provided with a plurality ofsub-regions; and a differential information storage region for storingthe differential information relating to the primary logical volume. Thedifferential information includes a set value indicating whether or notthere is a difference between the primary logical volume and thesecondary logical volume, with respect to the data stored in each of theplurality of sub-regions in the primary logical volume. The controlsection refers to the differential information, and does not create thedata set for particular data, if the set value corresponding to the dataindicates that there is no difference.

The data processing system according to a second aspect of the presentinvention comprises: a first storage system for storing data; and asecond storage system connected to the first storage system, forreceiving and storing data from the first storage system. The firststorage system comprises: a data set storage region for storing a dataset containing the data and update data for managing the data; and acontrol section for generating the data set containing update data formanaging the data, storing the generated data set in the data setstorage region, and sending a data set in the data set storage region tothe second storage system. The data set storage region is divided into aplurality of storage regions including a first storage region and asecond storage region. The data comprises first data and second data.The control section generates a first data set containing the first dataand first update data, being update data for the first data; stores atleast the first data of the generated first data set in the firststorage region; generates a second data set containing the second dataand second update data, being update data for the second data; andstores at least the second data of the generated second data set in thesecond storage region, being a separate storage region from the firststorage region.

The data processing method according to third aspect of the presentinvention is a data processing method implemented by a data processingsystem comprising a first storage system for storing data, and a secondstorage system connected to the first storage system, for receiving andstoring data from the first storage system, comprising: a step wherebythe first storage system generates a first data set containing firstdata and first update data, being update data for the first data; a stepwhereby the first storage system stores at least the first data of thegenerated first data set, in a first storage region of a plurality ofstorage regions constituting a data storage region; a step whereby thefirst storage system generates a second data set containing second dataand second update data, being update data for the second data; a stepwhereby the first storage system stores at least the second data of thegenerated second data set in a second storage region contained in theplurality of storage regions, being a separate storage region to thefirst storage region; a step whereby the first storage system sends afirst data set in the first storage region and a second data set in thesecond storage region, to the second storage system; and a step wherebythe second storage system receives the first data set and the seconddata set from the first storage system, and stores the first data setand second data set thus received, in a data set storage region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the logical composition according toone mode of implementing the present invention;

FIG. 2 is a block diagram of the storage system in one mode ofimplementing the present invention;

FIG. 3 is a diagram illustrating the relationship between updateinformation and write data in one mode of implementing the presentinvention;

FIG. 4 is a diagram showing an example of volume information in one modeof implementing the present invention;

FIG. 5 is a diagram showing an example of pair information in one modeof implementing the present invention;

FIG. 6 is a diagram showing an example of group information in one modeof implementing the present invention;

FIG. 7 is a diagram showing an example of pointer information in onemode of implementing the present invention;

FIG. 8 is a diagram showing the structure of a journal logical volume inone mode of implementing the present invention;

FIG. 9 is a flowchart showing a procedure for starting replication ofdata according to one mode of implementing the present invention;

FIG. 10 is a flowchart for describing an initial copy process in onemode of implementing the present invention;

FIG. 11 is a diagram for describing a command reception process in onemode of implementing the present invention;

FIG. 12 is a flowchart of a command reception process in one mode ofimplementing the present invention;

FIG. 13 is a flowchart of a journal creation process in one mode ofimplementing the present invention;

FIG. 14 is a diagram for describing a journal read reception process inone mode of implementing the present invention;

FIG. 15 is a flowchart of a journal read reception process in one modeof implementing the present invention;

FIG. 16 is a diagram for describing a journal read command process inone mode of implementing the present invention;

FIG. 17 is a flowchart of a journal read command process in one mode ofimplementing the present invention;

FIG. 18 is a flowchart of a journal storage process in one mode ofimplementing the present invention;

FIG. 19 is a diagram for describing a restore process in one mode ofimplementing the present invention;

FIG. 20 is a flowchart of a restore process in one mode of implementingthe present invention;

FIG. 21 is a diagram showing an example of update information in onemode of implementing the present invention;

FIG. 22 is a diagram showing an example of update information in ajournal creation process, according to one mode of implementing thepresent invention;

FIG. 23 shows an overview of a compositional example of a dataprocessing system relating to a first embodiment of one mode ofimplementing the present invention;

FIG. 24 shows an example of the composition of the pointer information700A in the first embodiment of one mode of implementing the presentinvention;

FIG. 25 shows the composition of the pointer information 700Aillustrated in FIG. 24, showing the composition of this information in aplurality of journal logical volumes #1A, #2A, #3A;

FIG. 26 shows an example of the composition of the pointer information700A in a first modification of the first embodiment of one mode ofimplementing the present invention;

FIG. 27 shows an example of the composition of a plurality of journallogical volumes, #1A, #2A, #3A in a second embodiment of one mode ofimplementing the present invention;

FIG. 28 shows an example of the composition of extent information formanaging a plurality of extents, in a second embodiment of one mode ofimplementing the present invention;

FIG. 29 shows an example of the composition of pointer information 700Acorresponding to FIG. 27 and FIG. 28;

FIG. 30 shows a portion of an initial copy process in a third embodimentof one mode of implementing the present invention;

FIG. 31A shows a first GUI screen;

FIG. 31B shows a second GUI screen;

FIG. 32A shows a third GUI screen;

FIG. 32B shows a fourth GUI screen;

FIG. 33A shows a fifth GUI screen;

FIG. 33B shows a sixth GUI screen;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Below, one mode of implementing the present invention and severalembodiments based on this mode of implementation are described withreference to the drawings. Firstly, the basic features of dataprocessing using journals is described with reference to FIG. 1 to FIG.22, as one mode of implementing the present invention. Thereupon,applications of this data processing will be described with reference toFIG. 23 onwards, as embodiments based on this mode of implementation.

FIG. 1 is a block diagram showing an overview of the logical compositionof a data processing system relating to one mode of implementing thepresent invention.

The data processing system 1 is constituted by connecting a hostcomputer 180 and a storage system 100A, by means of a connection path190, and by connecting the storage system 100A and a storage system 100Bfor holding a replica of the data stored in the storage system 100A, bymeans of a connection path 200. In the following description, in orderto make a ready distinction between the storage system 100A holding thedata to be replicated (in other words, the original data), and thestorage system 100B holding the replica data, the storage system 100Aholding the data to be replicated is called the “primary storage system100A”, and the storage system 100B holding the replica data is calledthe “secondary storage system 100B”. Furthermore, the term “storagesystem 100” may be used simply to refer to either 100A or 100B.Furthermore, the storage region of a storage system 100 is managed bydividing it up into separate regions, and these divided storage regionsare called “logical volumes”.

A storage system 100 comprises a plurality of logical volumes 230. Thecapacity of the logical volumes 230 and their physical storage positions(physical addresses) in the storage system 100 can be determined bymeans of a maintenance terminal, such as a computer connected to thestorage system 100, or by means of the host computer 180. The physicaladdress of each logical volume 230 is stored in volume information 400(see FIG. 4), which is described hereinafter. The physical addresscomprises, for example, a number (storage device number) identifying astorage device inside the storage system 100 (for example, a hard diskdrive), and a numerical value which uniquely identifies a storage regionin that storage device, for example, a position from head position ofthe storage region of the storage device. In the following description,the physical address is taken to be a set comprising a storage devicenumber and a position from the head of the storage region of the storagedevice. Furthermore, in the following description, the logical volume230 is a storage region in one storage device, but it is also possibleto make one logical volume correspond to storage regions in a pluralityof storage devices, by converting (in other words, associating) thelogical address and the physical address.

When referencing or updating data stored in a storage system 100, thenumber identifying a logical volume 230 (a logical volume number) andthe numerical value uniquely identifying the storage region, forexample, the position from the head of the storage region of the logicalvolume 230, can be specified universally, and hereinafter, a setcomprising a logical volume number and a position from the head of thestorage region of a logical volume 230 (the position at the logicaladdress), is called the “logical address”.

In the following description, in order to distinguish readily betweenthe data to be replicated and the replica data, a logical volume storingdata to be replicated is called a “primary logical volume” and a logicalvolume stored replica data is called a “secondary logical volume”.Furthermore, a pair comprising a primary logical volume and a secondarylogical volume is called a “pair”. The relationships, states, and thelike, of the primary logical volumes and the secondary logical volumesare included in path information 500 (see FIG. 5), describedhereinafter.

In order to maintain the update sequence of the data between therespective logical volumes 230, management units known as groups areprovided. For example, the host computer 180 updates first data in theprimary logical volume (DATA1) 230 and then reads out that first data,and carries out processing for updating a second data in the primarylogical volume (DATA2) 230, using the numerical value of the first data.If the replication processing for copying data from the primary logicalvolume (DATA1) 230 to the secondary logical volume (COPY1) 230 iscarried out independently from the replication processing for copyingdata from the primary logical volume (DATA2) 230 to the secondarylogical volume (COPY2) 230, then the replication processing for copyingthe second data to the secondary logical volume (COPY2) 230 may becarried out before the replication processing for copying the first datato the secondary logical volume (COPY1) 230. If the replicationprocessing for copying the first data to the secondary logical volume(COPY1) 230 is halted due to a fault, or the like, between thereplication processing for copying the second data to the secondarylogical volume (COPY2) 230 and the replication processing for copyingthe first data to the secondary logical volume (COPY1) 230), then thedata in the secondary logical volume (COPY1) 230 and the data in thesecondary logical volume (COPY2) 230 will become mutually inconsistent.In order to maintain consistency between the data in the secondarylogical volume (COPY1) 230 and the secondary logical volume (COPY2) 230even in cases of this kind, the logical volumes 230 which are requiredto preserve the data update sequence are registered in the same group,and each time the data is updated, an update number is assigned in thegroup information 600 (see FIG. 6), described hereinafter, and data isreplicated to the secondary logical volume in the order of the updatenumbers. For example, in FIG. 1, the logical volume (DATA1) 230 and thelogical volume (DATA2) 230) of the primary storage system 100Aconstitute group 1. The logical volume (COPY1) 230, which is a replicaof the logical volume (DATA1) 230, and the logical volume (COPY2) 230which is a replica of the logical volume (DATA2) 230, constitute group 1in the secondary storage system 100B.

In order to update the data in the secondary logical volume when thedata in the primary logical volume is updated, the primary storagesystem 100A creates a journal (described hereinafter), which it storesin a logical volume 230 in the primary storage system 100A. In thepresent mode of implementation, in each group, a logical volume forsaving only the journal for that group (hereinafter, called the “journallogical volume”) 230 is provided. In FIG. 1, the journal logical volume(JNL1) 230 is allocated to group 1 in the primary storage system 100A,and the journal logical volume (JNL2) 230 is allocated to group 1 in thesecondary storage system 100B.

The journal logical volume (JNL2) 230 stores a journal transferred fromthe primary storage system 100A to the secondary storage system 100B. Bysaving the journal in the journal logical volume (JNL2) 230, forexample, if the load on the secondary storage system 100B is high, thenit is possible to update the data in the secondary logical volume 100Bafter a time has passed and the load on the secondary storage system100B has reduced, rather than updating the data in the secondary logicalvolume 100B when the journal is received. Moreover, if there are aplurality of connection paths 200, then multiple journals aretransferred from the primary storage system 100A to the secondarystorage system 100B in a superimposed fashion, in such a manner that thetransfer capacity of the connection paths 200 can be used efficiently.In order to preserve the update sequence, it is possible that a largenumber of journals may accumulate in the secondary storage system 100B,but the cache memory (described hereinafter) can be released bywithdrawing any journals that cannot be used immediately for updatingthe data in the secondary logical volume, to the journal logical volume(JNL2) 230.

A journal contains the same write data as that stored in other logicalvolumes apart from the journal logical volume (for example, the primarylogical volume or the secondary logical volume), and update information.“Write data” means data to be written that is transmitted together witha write command from the host computer 180. “Update information” isinformation for managing that write data, and as illustrated in FIG. 21,for example, it includes the time at which the write command wasreceived, the group number, the update data of the group information 600(described hereinafter), the logical address of the write command, thedata size of the write data, and the logical address of the journallogical volume storing the write data, and the like. The updateinformation may also store only one of either the time at which thewrite command was received, or the update number. If there is a writecommand creation time in a write command from the host computer 180,then the creation time in this write command may be stored instead ofthe time at which the write command was received.

An example of the update information in a journal is described now withreference to FIG. 3 and FIG. 21. Below, the position from the head of astorage region of the logical volume 230 (in other words, a positionwith reference to the head position), is called an “address”, for thesake of convenience.

According to the update information 310 illustrated in FIG. 21, it canbe seen that a write command was received at 22:22:10 (hr:min:sec) onMar. 17, 1999. Furthermore, it can also be gathered that this writecommand is a command indicating that the write data is to be writtenstarting from the address 700 of the logical volume 230 having thelogical volume number “1”, and the data size of the write data is 300Furthermore, it can also be seen that the write data contained in thejournal is to be written starting from the address 1500 in the journallogical volume 230 having a logical volume number of “4”. Moreover, itcan also be gathered that the logical volume 230 having a logical volumenumber of “1” belongs to group 1, and that this update is the fourthdata update since the start of data replication for group 1.

As shown in FIG. 3, for example, the journal logical volume is used bybeing divided into a storage region for storing update information (anupdate information region), and a storage region for storing write data(a write data region), (incidentally, the symbol “#4” indicates that thelogical volume number is “4”. The update information is stored in theupdate information region, in update number order, starting from thehead of the update information region, and when the end of the updateinformation region is reached, the update information having the nextupdate number is stored, starting from the head of the updateinformation region. Write data is stored in the write data region, insequence, starting from the head of the write data region, and when theend of the write data region is reached, then the next write data isstored starting from the head of the write data region. The ratio of thesize of the update information region to the size of the write dataregion may be a fixed ratio, or it may be a variable ratio set by meansof a specific terminal, such as the maintenance terminal, the hostcomputer 180, or the like. This information can be included in thepointer information 700 (see FIG. 7), which is described hereinafter. Inthe following description, the journal logical volume is divided into anupdate information region and a write data region for use, but it isalso possible to adopt a method wherein the journal, in other words, aset of update information and write data, is stored in a continuousfashion, starting from the head of the logical volume.

Furthermore, one example of an operation for reflecting a data updatemade to a primary logical volume of the primary storage system 100A, ina secondary logical volume of the secondary storage system 100B, will bedescribed broadly with reference to FIG. 1.

(1) When the primary storage system 100A receives a write commandrelating to the data in the primary logical volume (DATA1) 230, from thehost computer 180, it updates the data in the primary logical volume(DATA1) 230 and saves a journal in the journal logical volume (JNL1)230, by means of a command reception process 210 and a read/writeprocess 220, which are described hereinafter (270 in FIG. 1).

(2) The secondary storage system 100B reads out the journal from theprimary storage system 100A, by means of a journal read process 240,described hereinafter, and it saves the journal in the journal logicalvolume (JNL2) 230, by means of a read/write process 220 (280 in FIG. 1).

(3) When the primary storage system 100A receives a command for readingthe journal from the secondary storage system 100B, it reads out thejournal from the journal logical volume (JNL1) 230 and transmits it tothe secondary storage system 100B, by means of a command receptionprocess 210 and a read/write process 220, as described hereinafter (280in FIG. 1).

(4) Using the pointer information 700, the secondary storage system 100Breads out the journal from the journal logical volume (JNL2) 230, insequence with the update number, and updates the data in the secondarylogical volume (COPY1) 230, by means of a restore process 250 and aread/write process 220 (290 in FIG. 1).

FIG. 2 is a block diagram showing an example of the composition of theprimary storage system 100A. Below, for the sake of convenience, it issupposed that the primary storage system 100A and the secondary storagesystem 100B have similar compositions, and the primary storage system100A is taken as a representative example to describe the composition ofthe storage systems 100. However, the primary storage system 100A andthe secondary storage system 100B do not necessarily have to be of thesame composition.

The primary storage system 100A is a disk array system, such as a RAID(Redundant Array of Independent Disks) system, for example. The primarystorage system 100A comprises, for example, a control sub-system 101 forcontrolling the processing carried out by the primary storage system100A, a RAID group 210, and a service processor (SVP) 281. The controlsub-system 101 comprises, for example, a plurality of DKAs (hereinafter,DKA) 120, a plurality of channel adapters (hereinafter, CHA) 110, acache memory 130, a shared memory 140 and a switching control section270.

The RAID group 210 comprises a plurality of storage devices 150, forexample, it provides redundant storage based on RAIDs, such as a RAID1or RAID5 system. The respective storage devices 150 can be constitutedby storage devices, such as a hard disk drive (or a disk device itself),a semiconductor memory device, a magneto-optical disk drive (or amagneto-optical disk itself), and the like. At least one or more logicalvolumes 230 forming logical storage regions can be set in the physicalstorage regions provided by the respective storage devices 150. Aplurality of data used by the host computer 180 can be stored in thelogical volumes 230. Moreover, it is also possible to store controlinformation, and the like, in a separate logical volume 230, and to usesame as a system region. Furthermore, the storage devices 150 do not allhave to be positioned inside the frame of the primary storage system100A. For example, it is possible to use a logical volume belonging toanother storage system (not illustrated) as a logical volume of theprimary storage system 100A. In the following description, there may becases where logical volume is abbreviated to “volume”.

The respective DKAs 120 control data transmission and reception betweenthe respective storage devices 150. Each of the DKAs 120 may beconstituted by a microcomputer system comprising a CPU, ROM, RAM, andthe like, for example. A plurality of DKAs 120 are provided in theprimary storage system 100A. The DKAs 120 transfer block-level databetween the storage devices 150, on the basis of a SCSI or iSCSIprotocol, or the like.

Similarly to the DKAs 120, each of the plurality of CHAs 110 may beconstituted by a microcomputer system. A plurality of host CHAs 110A forperforming data communications with the host computer 180 via theconnection path 190, and one or more system CHA 110B for performing datacommunications with the other storage systems 100 via the connectionpath 200, are included in the plurality of CHAs 110. At least one of theconnection paths 190 and 280 may be a communications network, or it maya dedicated path line. Furthermore, the host CHAs 110A may be preparedrespectively in accordance with the type of host computer 180 (forexample, whether it is a server or a main frame device, or the like).

The cache memory 130 may be constituted by a volatile or a non-volatilesemiconductor memory, for example. The cache memory 130 stores writedata (data written to the logical volume) from the host computer 180.Moreover, the cache memory 130 stores data read out from the logicalvolume 230 (hereinafter, called “read data”).

The shared memory 140 may be constituted by a non-volatile or volatilesemiconductor memory, for example. The shared memory 140 stores, forexample, various commands received from the host computer 180, andcontrol information, and the like, used to control the primary storagesystem 100A. The commands and control information, and the like, may bestored in a redundant fashion by means of a plurality of shared memories140. The cache memory 130 and the shared memory 140 may be constructedas mutually separate memories, or alternatively, a portion of a singlememory may be used as a cache memory region and the remaining portion ofthe memory may be used as a shared memory region.

The switching control section 270 is connected respectively to thevarious DKAs 120, the host CHA 110A, the system CHA 110B, the cachememory 130, and the shared memory 140. The switching control section 270may be constituted by an ultra-high-speed cross-bar switch, or the like,for example.

The SVP 281 gathers and monitors the states of the respective sectionsof the primary storage system 100A, via an internal network (such as aLAN) 282, for example. The SVP 280 may output the gathered data relatingto the internal states, either directly as raw data, or as processedstatistical data, to an external management terminal (not illustrated).Examples of information which may be gatherable by the SVP 280 include:the device composition, power supply alarms, temperature alarms,input/output speed, and the like. The system administrator can changethe settings of the RAID composition, or implement processing forshutting off various types of packages (for example, the CHAs 110 andthe DKAs 120), from the management terminal, via the SVP 280.

Next, one example of the processing carried out by the primary storagesystem 100A will be described. The host CHA 110A receives write commandsand write data from the host computer 180, via the connection path 190.The write command thus received is stored in the shared memory 140, andthe write data thus received is stored in the cache memory 130. The DKAs120 refer to the shared memory 140 at regular intervals. When the DKA120 discovers an unprocessed write command stored in the shared memory140, then it reads out the write data from the cache memory 130, andperforms address conversion, and the like, in accordance with this writecommand. The DKA 120 stores the write data in the respective storagedevices 150 which constitute the logical volume 230 designated by thewrite command.

A case where a read command from the host computer 180 is processed isnow described. When a host CHA 110A receives a read command from thehost computer 180, it stores that read command in the shared memory 140.If the DKA 120 discovers an unprocessed read command in the sharedmemory 140, then it reads out data from the respective storage devices150 constituting the logical volume 230 designated by the read command.The DKA 120 stores the data thus read out in the cache memory 130.Furthermore, the DKA 120 reports that read out of the requested data hasbeen completed, to the host CHA 110A, via the shared memory 140. Thehost CHA 110A reads in data from the cache memory 130 and transmits thisto the host computer 180.

One example of data replication (hereinafter, also called “remotecopying” in some cases) performed between the primary storage system100A and the secondary storage system 100B, via the connection path 200(which may also be called a “remote copy line”) will now be described.Remote copying does not involve a write command or a read command fromthe host computer 180, but rather is a data replication process carriedout in response to write commands and read commands transmitted andreceived between the storage systems 100A and 100B, without requiringthe intervention of the host computer 180.

More specifically, for example, if the control sub-system 101A of theprimary storage system 100A is writing write data to the primary logicalvolume (DATA1) 230 which forms a pair with the secondary logical volume(COPY1) 230, then it transmits the write data and the correspondingwrite command to the secondary storage system 100B, via the connectionpath 200. Thereby, the updated data is stored in the secondary storagesystem 100B in synchronism with the updating of the data.

Furthermore, the control sub-system 101A of the primary storage system100A generates, every time the primary logical volume (DATA 1) isupdated, a journal as described above and stores it in the journallogical volume (JNL1) 230, for example, and if it receives a readcommand from the secondary storage system 100B (or if it has issued awrite command to the secondary storage system 100B), then the journal inthe journal logical volume (JNL1) 230 is transmitted to the secondarystorage system 200B, via the connection path 200. Consequently, thejournal is stored in the secondary storage system 100B in anon-synchronized fashion with respect to the storage of the journal inthe primary storage system 100A. Furthermore, by carrying out a restoreprocess in the secondary storage system 100B using this journal, thesecondary logical volume (COPY1) 230 becomes a replica of the primarylogical volume (DATA1) 230.

The foregoing provides an example of the composition of a storage devicesystem 100 according to the present mode of implementation. Needless tosay, it is not necessary to limit the storage system 100 to theaforementioned composition. For example, the control sub-system 101 isnot limited to the aforementioned composition, and it may, for example,be constituted by a memory capable of storing control information, writedata, and the like, an interface device for communicating with the hostcomputer (hereinafter, abbreviated as “I/F”), an I/F for communicatingwith the other storage systems, an I/F for communicating with thestorage devices 150, and a control section (for example, a CPU) forcontrolling communications via these I/F, and the like, on the basis ofthe information in the memory. Moreover, in the storage system 100, afirst data transfer performed from the host computer 180 (or anotherstorage system) to the cache memory 130, via a CRA 110 and the switchingcontrol section 270, and the second data transfer performed from thecache memory 130 to the host computer (or another storage system) viathe switching control section 270 and a CHA 110, can be carried outsimultaneously, provided that the CHA 110 controlling the first datatransfer and the CHA 110 controlling the second data transfer aredifferent and/or provided that the caches forming the transfer sourceand the transfer destination of the data are different (for example,provided that the cache memory address of the transfer source isdifferent from the cache memory address of the transfer destination).Similarly, in the storage system 100, a third data transfer performedfrom a storage device 150 to the cache memory 130, via a DKA 120 and theswitching control section 270, and a fourth data transfer performed fromthe cache memory 130 to a storage device 150 via the switching controlsection 270 and a DKA 120, can be carried out simultaneously, providedthat the DKA 120 controlling the third data transfer and the DKA 120controlling the fourth data transfer are different and/or provided thatthe caches forming the transfer source and the transfer destination ofthe data are different (for example, provided that the cache memoryaddress of the transfer source is different from the cache memoryaddress of the transfer destination). Moreover, the first data transferor the second data transfer, and the third data transfer and/or thefourth data transfer can be carried out simultaneously, provided thatthe transfer destination in the first data transfer or the transfersource in the second data transfer is different from the transferdestination in the third data transfer and/or the transfer source in thefourth data transfer. Moreover, in order to perform synchronizedtransfer of this kind, the respective transmission paths (for example,the transmission path between the CHA 110 and the switching controlsection 270, the transmission path between the DKA 120 and the switchingcontrol section 270, and the transmission path between the switchingcontrol section 270 and the cache memory 130) must have suitablebandwidth (transmission speed). If, for example, one switching controlsection 270 is connected to two CHAs 110, two DKAs 120 and two cachememories 130, then if the bandwidth between the switching controlsection 270 and the cache memories 130 is not equal to or greater thanthe bandwidth between the CHAs 110 (or DKAs 120) and the switchingcontrol section 270, there will be no merit is using superimposedtransmission, and hence it is desirable that this bandwidth is two ormore times the bandwidth between the CHAs 110 (or DKAs 120) and theswitching control section 270. Furthermore, the write speed and read outspeed of the storage device 150 and the write speed and read out speedof the cache memory 130 should be faster speeds than the transfer speedon the path between the storage device 150 and the cache memory 130, anddesirably, they are speeds which will not cause under-run errors orover-run errors between these elements.

The volume information 400, path information 500, group information 600and pointer information 700 are stored as types of control informationin a memory which can be referenced by the CHA 110 and the DKA 120, suchas the shared memory 140, for example. These items are described below.

FIG. 4 shows an example of the composition of volume information 400.

The volume information 400 is information for managing a plurality oflogical volumes 230, and comprises information elements indicating thelogical volume number associated with each logical volume, the volumestatus, the volume format, the capacity (in units of gigabytes, forexample), the pair number, and the physical address.

The volume status for each logical volume is an information elementwhich indicates the status of that logical volume, for example:“normal”, “primary”, “secondary”, “abnormal”, “unused”, or the like. Alogical volume 230 having a volume status of “normal” or “primary” is alogical volume 230 which can be accessed normally by the host computer180. A logical volume 230 having a volume status of “secondary” is alogical volume 230 to which access from the host computer 180 may bepermitted. A logical volume 230 having a volume status of “primary” is alogical volume for which data replication is carried out (in otherwords, a primary logical volume) 230. A logical volume 230 having avolume status of “secondary” is a logical volume used to replicate data(in other words, a secondary logical volume) 230. A logical volume 230having a volume status of “abnormal” is a logical volume 230 whichcannot be accessed normally, due to a problem. Here, a “problem” means,for example, a problem in the disk drive 110 which holds the logicalvolume 230. A logical volume 230 having a volume status of “unused”indicates a logical volume 230 that is not being used.

The pair number for each logical volume is a number for identifying apair consisting of a primary logical volume and a secondary logicalvolume. More specifically, the pair number for each logical volume is apair number for identifying path information 500 (describedhereinafter), which is valid when the volume status corresponding tothat logical volume is “primary” or “secondary”.

According to the volume information 400 illustrated in FIG. 4, forexample, the logical volume 230 having a logical volume number of “1” isa primary logical volume (in other words, a logical volume whose data isreplicated) having a format type of “OPEN3” and a storage capacity of 3GB, which stores data from the head position of the storage region ofthe storage device 150 having a storage device number of “1”, and whichis accessible. In addition to containing information relating to theplurality of logical volumes 230 in the storage system 100 where thatvolume information 400 is provided, the volume information 400 may alsorecord information relating to one or more logical volumes 230 inanother storage system 100 connected to that storage system 100 via theconnection path 200.

FIG. 5 shows an example of the composition of path information 500.

The path information 500 is information for managing pairs, whichincludes information elements indicating, for example, the pair numberassociated with each pair, the pair status, the primary storage systemnumber, the primary logical volume number, the secondary storage systemnumber, the secondary logical volume number, the group number, and thecopied address.

The pair status for each pair is an information element indicating thestatus of that pair, which may be, for example, “normal”, “abnormal”,“unused”, “not copied”, “copying”, or the like. A pair status of“normal” indicates that data replication of the primary logical volume230 has been carried out normally. A pair status of “abnormal” indicatesthat replication of the primary logical volume 230 has not been carriedout, due to a problem. Here, a “problem” means an interruption of theconnection path 200, for example. A pair status of “unused” indicatesthat the pair number information corresponding to that pair status isnot valid. A pair status of “copying” indicates that initial copyprocessing, as described below, is in progress. A pair status of “notcopied” indicates that initial copy processing, as described below, hasnot yet been carried out.

The primary storage system number for each pair is a number indicatingthe primary storage system 100A holding the primary logical volume 230constituting that pair.

The secondary storage system number for each pair is a number indicatingthe secondary storage system 100B holding the secondary logical volume230 constituting that pair.

If the storage system 100 providing the path information 500 is theprimary storage system 100A, then the group number for the pair will bethe group number of the group to which the primary logical volume 230constituting that pair belongs, and if the storage system 100 providingthe path information 500 is a secondary storage system, then it will bethe group number of the group to which the secondary logical volume 230constituting that pair belongs.

The copied address for each pair is described hereinafter with referenceto the initial copy processing.

According to the path information 500 illustrated in FIG. 5, forexample, the pair having a pair number of “1” is a pair constituted by aprimary logical volume having a logical volume number of “1” and asecondary logical volume having a logical volume number of “1”, and itcan be seen that data replication processing has been carried outnormally.

FIG. 6 shows an example of the composition of group information 600.

The group information 600 is information for managing one or more groupsconstituted by a plurality of logical volumes 230, and it containsinformation elements indicating, for example, the group numberassociated with each group, the group status, the set of pairs, thejournal logical volume number and the update number.

The group status for each group is an information element whichindicates the status relating to that group, for example: “normal”,“abnormal”, “unused”, or the like. A group status of “normal” indicatesthat the pair status of at least one of the pairs identified by the pairset associated with that group is “normal”. A group status of “abnormal”indicates that the pair status of all of the pairs identified by thepair set associated with that group is “abnormal”. A group status of“unused” indicates that the group number information for thecorresponding group is not valid.

The pair set for each group includes the pair numbers of the pairsformed by the respective logical volumes in that group. If the storagesystem 100 having this group information 600 is a primary storage system100A, then the pair set includes all of the pair numbers correspondingrespectively to all of the primary logical volumes belonging to thatgroup. If, on the other hand, the storage system 100 having this groupinformation 600 is a secondary storage system 100B, then the pair setincludes all of the pair numbers corresponding respectively to all ofthe secondary logical volumes belonging to that group.

The journal logical volume number for each group indicates a number foridentifying the journal logical volume belonging to that group.

The update number for each group is a number set in the updateinformation of the journal, which is used in order to preserve the dataupdate sequence, in the secondary storage system 100B. The update numberof a group has an initial value of 1, but if data is subsequentlywritten to a primary logical volume in that group, then 1 is added tothe update number corresponding to that group only.

Supposing that the group information 600 illustrated in FIG. 6 is groupinformation provided in a primary storage system 100A, for example, thenaccording to this group information, it can be seen that the grouphaving a group number of “1” contains a primary logical volumeconstituting a pair having a pair number of “1”, a primary logicalvolume constituting a pair having a pair number of “2”, and a journallogical volume having a logical volume number of “4”. Moreover, it canalso be seen that data replication processing for the group having agroup number of “1” has been carried out normally.

FIG. 7 shows an example of the composition of pointer information 700.FIG. 8 shows the contents that are identified by the pointer information700 shown in FIG. 7.

As illustrated in FIG. 7, the pointer information 700 is prepared foreach group, and is used to manage the journal logical volume containedin the corresponding group. The pointer information 700 containsinformation elements indicating, for example, an update informationregion head address, a write data region head address, a newest updateinformation address, an oldest update information address, a newestwrite data address, an oldest write data address, a read start address,and a retry start address.

The update information region head address is the logical address of thehead position of the storage region storing the update information ofthe journal logical volume (the update information region).

The write data region head address is the logical address of the headposition of the storage region storing the write data of the journallogical volume (the write data region).

The newest update information address is the logical address of the headposition used to store the update information in a journal, when thenext journal is stored (in other words, information indicating where tostart writing the update information contained in the next journal).

The oldest update information address is the logical address of the headposition of the region where the update information of the oldestjournal (namely, the journal having the smallest update number) isstored.

The newest write data address is the logical address of the headposition used to store the write data in a journal, when the nextjournal is stored (in other words, information indicating where to startwriting the write data contained in the next journal).

The oldest write data address is the logical address of the headposition of the region where the write data in the oldest journal(namely, the journal having the smallest update number) is stored.

The read start address and the retry start address are informationelements used only by the primary storage system 100A. This informationis used in journal read reception processing, which is describedhereinafter. A detailed description of the read start address and theretry start address is given below.

According to the pointer information 700 illustrated in the example inFIG. 7 and FIG. 8, it can be seen that the region for storing the updateinformation in the journal (the update information region) is the rangefrom address 0 (the head position) of journal logical volume #4 toaddress 699 of same, and the region for storing the write data in thejournal (the write data region) is the range from address 700 of journallogical volume #4 to address 2699 of same. Moreover, it can also be seenthat the update information of a journal is stored in the range betweenaddress 200 and address 499 of journal logical volume #4, and the updateinformation of the next journal is written from address 500 of journallogical volume #4 onwards. Furthermore, it can also be seen that thewrite data of the journal is stored in the range between address 1300and address 2199 of journal logical volume #4, and the write data of thenext journal is written from address 2200 of journal logical volume #4onwards.

The foregoing provides an example of the composition of the pointerinformation 700. In the description of the present mode ofimplementation, a configuration is described wherein one journal logicalvolume is allocated to each group, but it is also possible to allocate aplurality of journal logical volumes to one group. More specifically,for example, it is also possible to allocate two journal logical volumesto one group, provide pointer information 700 for each journal logicalvolume (or include information elements relating to the plurality ofjournal logical volumes in the pointer information 700), and storejournals in the journal logical volumes in alternating fashion. Thereby,it is possible to distribute the task of writing journals to the harddisk 150, and hence improved performance can be anticipated. Moreover,journal read out performance can also be improved. As a further concreteexample, it is also possible to allocate two journal logical volumes toone group, only one of the journal logical volumes being used in normalconditions, and the other journal logical volume being used in caseswhere the performance of the first journal logical volume in use hasdeclined. An example of a decline in performance is a case where thejournal logical volume is constituted by a plurality of storage devices150, data being stored by a RAID5 method, and one of that plurality ofstorage devices 150 suffers a fault.

Furthermore, the volume information 400, path information 500, groupinformation 600 and pointer information 700, and the like, describedabove can be stored in the shared memory 140. However, the invention isnot limited to this, and this information may also be stored in aconcentrated or distributed fashion, in at least one of the cache memory130, the CHAs 110, the DKA 120, and the storage devices 150, forexample. Moreover, each storage system 100 may be provided with controlinformation relating at least to the other storage systems 100 withwhich it is able to communicate, (for example, at least one of thevolume information 400, path information 500, group information 600, andpointer information 700), in addition to the control informationrelating to itself. In this case, moreover, each time the controlinformation in one of the other storage systems 100 is updated, theupdated contents may be reflected in the control informationcorresponding to that other storage system 100, which is provided in thefirst storage system 100.

Next, one example of a procedure for starting data replication from aprimary storage system 100A to a secondary storage system 100B isdescribed with reference to FIG. 9.

(1) A group creation step (step 900) is now described.

The user refers to the group information 600 of the primary storagesystem 100A, by means of a maintenance terminal or the host computer180, and acquires a group number A that has a group status of “unused”.The user designates the group number A and issues a group creationinstruction to the primary storage system 100A, by means of the SVP 281or the host computer 180. Upon receiving the group creation instruction,the primary storage system 100A changes the group status of thedesignated group number A (the group status in the group information 600held by primary storage system 100A) to “normal”.

Similarly, the user refers to the group information 600 of the secondarystorage system 100B and acquires a group number B having a group statusof “unused”. The user designates the secondary storage system number andthe group number B, and issues a group creation instruction to theprimary storage system 100A, by means of the SVP 281 or the hostcomputer 180. The primary storage system 100A receives this secondarystorage system number, the group number B and the group creationinstruction, and it transfers the group number B and the group creationinstruction thus received to the secondary storage system 100B specifiedby the secondary storage system number thus received. The secondarystorage system 100B receives the group creation instruction and inresponse to this instruction, changes the group status of the receivedgroup number B (the group status in the group information 600 held bythe secondary storage system 100B) to “normal”. In a modificationexample, the user may also designate a group number B and issue a groupcreation instruction to the secondary storage system 100B, by means ofthe SVP 281 of the secondary storage system 100B, or by means of a hostcomputer 180 connected to the secondary storage system 100B.

(2) A pair registration step (step 910) is now described.

The user issues a pair registration instruction, specifying informationindicating a data replication object and information indicating a datareplication destination, to the primary storage system 100A, by means ofthe SVP 281 or the host computer 180. The “information indicating thedata replication object” is, for example, information containing thegroup number A of the group of the data replication object (in otherwords, the data replication source), and the primary logical volumenumber of the corresponding primary logical volume. The “informationindicating the data replication destination” is, for example,information containing the secondary storage system number of thesecondary storage system 100B holding the replica data, the secondarylogical volume number of the secondary logical volume holding thereplica data, and group number B of the group to which this secondarylogical volume belongs.

Upon receiving this pair registration instruction, the primary storagesystem 100A acquires a pair number having a pair status of “unused”,from the path information 500, and carries out the following processingwith respect to the various information elements corresponding to thepair number thus acquired (the various information elements constitutingthe path information 500 in the primary storage system 100A). In otherwords, the primary storage system 100A changes the information element“pair status” from “unused to “not copied”, sets the primary storagesystem number indicating the primary storage system 100A in theinformation element “primary storage system number”, sets the designatedprimary logical volume number in the information element “primarylogical volume number”, sets the designated secondary storage systemnumber in the information element “secondary storage system number”,sets the designated secondary logical volume number in the informationelement “secondary logical volume number”, and sets the designated groupnumber A in the information element “group number”. Furthermore, theprimary storage system 100A refers to the group information 600 providedinside that primary storage system 100A, adds the pair number acquiredabove to the pair set corresponding to the designated group number A,and changes the volume status corresponding to the designated primarylogical volume number (the volume status in the volume information 400provided in the primary storage system 100A) to “primary”.

The primary storage system 100A transmits the primary storage systemnumber indicating the primary storage system 100A, and the group numberB, primary logical volume number and secondary logical volume numberdesignated by the user, to the secondary storage system 100Bcorresponding to the secondary storage system number specified by theuser. The secondary storage system 100B acquires an unused pair numberfrom the path information 500, and carries out the following processingwith respect to the various information elements corresponding to thepair number thus acquired (the various information elements constitutingthe path information 500 in the secondary storage system 100B). In otherwords, the secondary storage system 100B sets the information element“pair status” to “not copied”, sets the primary storage system numberindicating the primary storage system 100A in the information element“primary storage system number”, sets the designated primary logicalvolume number in the information element “primary logical volumenumber”, sets the secondary storage system number indicating thesecondary storage system B in the information element “secondary storagesystem number”, sets the designated secondary logical volume number inthe information element “secondary logical volume number”, and sets thedesignated group number B in the information element “group number”.Furthermore, the secondary storage system 100B refers to the groupinformation 600 provided inside that secondary storage system 100B, addsthe pair number acquired above to the pair set corresponding to thedesignated group number B, and changes the volume status correspondingto the designated secondary logical volume number (the volume status inthe volume information 400 provided in the secondary storage system100B) to “secondary”.

The processing in step 910 described above is carried out for the pairsof all of the data replication objects.

In the foregoing description, the registration of a logical volume in agroup and the setting of pairs of logical volumes are carried outsimultaneously, but these processes may also be carried respectively atdifferent times.

(3) A journal logical volume registration step (step 920) is nowdescribed.

The user issues an instruction for registering a logical volume used forstoring a journal (a journal logical volume) in a group (a journallogical volume registration instruction), to the primary storage system100A, by means of the SVP 281 or the host computer 180. The journallogical volume registration instruction comprises a group number and alogical volume number, for example.

The primary storage system 100A registers the designated logical volumenumber as the journal logical volume number of the group information 600of the designated group number. The volume status of the volumeinformation 400 of this logical volume is set to “normal”.

Similarly, the user refers to the volume information 400 of thesecondary storage system 100B, by means of the SVP 281 or host computer180, and issues a journal logical volume registration instruction to theprimary storage system 100A, specifying a secondary storage systemnumber, a group number B and a logical volume number to be used as thejournal logical volume, to the primary storage system 100A. The primarystorage system 100A transfers the journal logical volume registrationinstruction, the group number B and the logical volume number thusreceived, to the secondary storage system 100B identified by thedesignated secondary storage system number. The secondary storage system100B refers to the group information 600 provided in that secondarystorage system 100B, and registers the received logical volume number asthe information element “journal logical volume number” corresponding tothe received group number B. Furthermore, the secondary storage system100B refers to the volume information 400 provided in that secondarystorage system 100B, and sets the information element “volume status”corresponding to the received logical volume number, to “normal”.

The user may also designate the group number and the logical volumenumber to be used as the journal logical volume, and issue a journallogical volume registration instruction to the secondary storage system100B, by means of a SVP 281 of the secondary storage system 100B or bymeans of a host computer 180 connected to the secondary storage system100B.

The processing in step 920 above is carried out with respect to all ofthe logical volumes used as journal logical volumes. The sequence ofstep 910 and step 920 does not have to a random sequence.

(4) A replication process start step (step 930) is now described.

The user designates a group number for starting a data replicationprocess, and issues a data replication process start instruction, to theprimary storage system 100A, by means of the SVP 281 or the hostcomputer 180. The primary storage system 100A refers to the pairinformation 400 provided in that primary storage system 100A, and setsall of the copied addresses for the designated group number to “0”.

The primary storage system 100A instructs the secondary storage system100B specified by the secondary storage system number corresponding tothe designated group number, to start a journal read process and arestore process, which are described hereinafter.

The primary storage system 100A starts an initial copy process describedhereinafter.

(5) An initial copy completion step (step 940) is now described.

When initial copying has finished, the primary storage system 100Areports the end of the initial copy process, to the secondary storagesystem 100B specified in step 930. The secondary storage system 100Brefers to the path information 500 held in that secondary storage system100B, and changes all of the pair statuses corresponding to thedesignated group number (the pair statuses of the secondary logicalvolumes) to normal”.

FIG. 10 is a flowchart of an initial copy process.

In the initial copy process, journals are created in unit sizes for thewhole storage region of the primary logical volume forming the datareplication object, in sequence from the head position of the storageregion, using the copied addresses in the path information 500. Thecopied address has an initial value of 0, and each time a journal iscreated, the data volume thus created is added to this value. In theinitial copy process, journals are created from the head position of thestorage region of the logical volume, until the address immediatelybefore the copied address. By carrying out an initial copy process, itis possible to transfer data that has not been updated in the primarylogical volume, to the secondary logical volume. In the followingdescription, the host CHA 110A in the primary storage system 100A isdescribed as implementing this processing, but it may also beimplemented by the DKA 120 instead.

(1) The host CHA 110A in the primary storage system 100A finds a primarylogical volume having a pair status of “not copied” in a pair belongingto the group being processed (hereinafter, called “primary logicalvolume A”), on the basis of the group information 600 and the pathinformation 500 in the primary storage system 100A, and it updates thepair status relating to the primary logical volume A thus found, to“copying”, and then repeats the subsequent processes (steps 1010 and1020). If primary logical volume A does not exist, then the host CHA110A ends processing (step 1030).

(2) At step 1020, if the logical volume A does exist, then the host CHA110A creates a journal for a unit size of data (for example, 1 MB ofdata). The journal creation process is described below (step 1040).

(3) The host CHA 110A adds the data size of the created journal to thecopied address (step 1050).

(4) The aforementioned processing is repeated until the copied addressreaches the capacity of the primary logical volume A (step 1060). If thecopied address is not equal to the capacity of the primary logicalvolume A, then this means that a journal has been created for the wholestorage region of the primary logical volume A, and hence the pairstatus is updated to “normal” and processing of another primary logicalvolume is started (step 1070).

In the aforementioned flowchart, the primary logical volumes aredescribed as being handled independently, but it is also possible forjournals to be processed simultaneously for a plurality of data storedrespectively in a plurality of primary logical volumes.

FIG. 11 illustrates the sequence of a command reception process 210, andFIG. 12 is a flowchart of a command reception process 210. FIG. 13 is aflowchart of a journal creation process. Below, an operation where theprimary storage system 100A receives a write command from the hostcomputer 180 to the primary logical volume 230 forming a datareplication object will be described with reference to FIGS. 11 to 13.Moreover, in the following description, it is assumed that there is oneprimary logical volume and one journal logical volume belonging to aparticular group of the primary storage system 100A, the primary logicalvolume being called “primary logical volume 230PA” and the journallogical volume being called “journal logical volume JA”.

(1) The host CHA 110A in the primary storage system 100A receives anaccess command from the host computer 180 (step 1200). The accesscommand contains a command, such as a read, write or journal readcommand (described hereinafter), a logical address relating to thecommand, a data volume, and the like. Below, the logical address in theaccess command is called logical address A, the logical volume number iscalled logical volume number A, the position in the logical volume iscalled logical volume position A, and the data volume is called datavolume A. Moreover, the logical volume designated by the logical volumenumber A is called logical volume A.

(2) The host CHA 110A examines the access command (steps 1210 and 1215).If the access command is found to be a journal read command in theinvestigation in step 1215, the journal read reception processingdescribed below is carried out (step 1220). If the access command is acommand other than a journal read command or a write command, forexample, a read command, then read processing is carried out inaccordance with that read command (step 1230).

(3) If the access command is found to be a write command in theinvestigation in step 1210, then the host CHA 110A refers to the volumeinformation 400 and examines the volume status of the logical volume A(step 1240). In the investigation in step 1240, if the volume status ofthe logical volume A is any status other than “normal” or “primary”,then this means that access to the logical volume A is not possible, andhence the host CHA 110A reports an abnormal termination to the hostcomputer 180 (step 1245).

(4) If the volume status of the logical volume A is found to be “normal”or “primary” in the investigation in step 1240, then the host CHA 110Areserves the cache memory 130 (or a storage region of a prescribed sizein that memory 130), and reports that preparations for data receptionhas been completed to the host computer 180. The host computer 180receives this report and transmits write data to the primary storagesystem 100A. The host CHA 110A receives the write data and stores it inthe cache memory 130 (step 1250, and 1100 in FIG. 11).

(5) The host CHA 110A refers to the volume status in the logical volumeA, and investigates whether or not the logical volume A is a datareplication object (in other words, whether it is a primary logicalvolume) (step 1260). If the volume status is found to be “primary” inthe investigation in step 1260, then this means that the logical volumeA is a data replication object, and hence the host CHA 110A performsjournal creation processing, as described hereinafter (step 1265).

(6) If the volume status is found to be “normal” in the investigation instep 1260, or if the journal creation process in step 1265 hascompleted, then the host CHA 110A issues a command to the DKA 120 inorder to issue the write data to the storage device 150 providing thelogical volume A (1140 in FIG. 11), and it reports completion to thehost computer 180 (steps 1270 and 1280). Thereupon, the DKA 120receiving the write command for the write data stores the write data inthe storage device 150 providing the logical volume A, by means of aread/write process 220 (1110 in FIG. 11).

Next, journal creation processing will be described.

(1) The host CHA 110A investigates the volume status of the journallogical volume 230 JA belonging to the group number corresponding to thelogical volume number A, on the basis of the volume information 400,path information 500 and group information 600 (step 1310). If thevolume status of the journal logical volume is found to be “abnormal” inthe investigation in step 1310, then this means that the journal cannotbe stored in that journal logical volume, and therefore the host CHA110A changes the group status to “abnormal” and terminates processing(step 1315). In this case, the host CHA 110A may carry out processingfor changing the journal logical volume to a normal logical volume, forexample.

(2) If the journal logical volume is found to be normal in theinvestigation in step 1310, then the host CHA 110A continues the journalcreation process. The contents of the journal creation process varydepending on whether it is implemented as part of an initial copyprocess, or as part of a command reception process (step 1320). If thejournal creation process is part of a command reception process, thenthe host CHA 110A implements the processing from step 1330 onwards. Ifthe journal creation process is part of an initial copy process, thenthe host CHA 110A implements the processing from step 1370 onwards.

(3) If the journal creation process is part of a command receptionprocess, then the host CHA 110A investigates whether or not the logicaladdress A that is to be written to has been processed in the initialcopy process (step 1330). If the pair status of the logical volume A is“not copied”, then this means that the journal creation process is to becarried out later in an initial copy process, and therefore the host CHA110A terminates the process without creating a journal (step 1335). Ifthe pair status of the logical volume A is “copying”, or if the copiedaddress is equal to or lower than the logical address position A, thenthis means that the journal creation process is to be carried out laterin an initial copy process, and therefore the host CHA 110A terminatesthe process without creating a journal (step 1335). In cases other thanthe foregoing, in other words, if the pair status of the logical volumeA is “copying” and the copied address is higher than the logical addressposition A, or if the pair status of the logical volume A is “normal”,then this means that the initial copy process has already beencompleted, and therefore the host CHA 110A continues the journalcreation process.

(4) Next, the host CHA 110A investigates whether or not a journal can bestored in the journal logical volume. More specifically, using thepointer information 700, the host CHA 110A examines whether or not thereexists unused space in the update information region (step 1340). If thenewest update information address and the oldest update informationaddress in the pointer information 700 are equal, then this means thatthere is no unused space in the update information region, and thereforethe host CHA 110A terminates the process as “failed to create journal”(step 1390).

If, in the investigation in step 1340, there is unused space in theupdate information region, then the host CRA 110A examines whether ornot it is possible to store write data in the write data region, on thebasis of the pointer information 700 (step 1345). If the sum of thenewest write data address and the data volume A is equal to or greaterthan the oldest write data address, then this means that the write datacannot be stored in the write data region, and therefore the host CHA110A terminates the process as “failed to create journal” (step 1390).

(5) If a journal can be stored, then the host CHA 110A acquires theupdate number corresponding to the group in question (the group to whichthe journal logical volume JA1 belongs) (the update number contained inthe group information 600), the logical address for storing the updateinformation and the logical address for storing the write data, and itcreates update information in the cache memory 130. Furthermore, thehost CHA 110A sets a numerical value equal to the acquired update numberplus 1, in the group information 600, as the new update number. Thelogical address for storing the update information is the newest updateinformation address in the pointer information 700, and the host CHA110A sets the value of this address plus the size of the updateinformation, as a fresh newest update information address in the pointerinformation 700. The logical address for storing the write data is thenewest write data address in the pointer information 700, and the hostCHA 110A sets the value of the newest write data address plus the datavolume A, as a fresh newest write data address in the pointerinformation 700.

The host CHA 110A sets the values and the group number acquired above,the timing at which the write command was received, the logical addressA in the write command, and the data volume A, in the update information(step 1350, 1120 in FIG. 11). For example, in the case of the groupinformation 600 shown in FIG. 6 and the pointer information 700 shown inFIG. 7, if a write command of data size 100 is received at the positionof the address 800 of the primary logical volume #1 belonging to group1, then update information such as that illustrated in FIG. 22 iscreated. The update number in the group information is 5, the newestupdate information address in the pointer information is 600 (taking thesize of the update information to be 100), and the newest write dataaddress is 2300.

(6) The host CHA 110A commands the DKA 120 to write the updateinformation and the write data in the journal to the storage device 150,and then terminates normally (step 1360; 1130, 1140, 1150 in FIG. 11).

(7) If the journal creation process is part of an initial copy process,then the host CHA 110A implements the processing from step 1370 onwards.The host CHA 110A investigates whether or not a journal can be created.More specifically, using the pointer information 700, the host CHA 110Aexamines whether or not there exists unused space in the updateinformation region (step 1370). If the newest update information addressand the oldest update information address in the pointer information 700are equal, then this means that there is no unused space in the updateinformation region, and therefore the host CHA 110A terminates theprocess as “failed to create journal” (step 1390). In the initial copyprocess described in the present mode of implementation, the write datain the journal is read from the primary logical volume, and since thewrite data region is not used, then it is not necessary to check forunused space in the write data region.

(8) If it is found from the investigation in step 1370 that a journalcan be created, then the host CHA 110A acquires the numerical valueestablished in the update information and creates update information inthe cache memory 130. The update number is acquired from the groupinformation 600 for the group in question, and the host CHA 110Aestablishes a value equal to this update number plus one, as a newupdate number in the group information 600. The logical address forstoring the update information is the position of the newest updateinformation address in the pointer information 700, and the host CHA110A sets the value of this address plus the size of the updateinformation, as the fresh newest update information address in thepointer information 700.

The host CHA 110A sets the values and group number acquired above, thestart time of the process, the logical address used in the initial copyprocess, the amount of data processed per operation in the initial copyprocess, the logical address of the journal logical volume storing thewrite data, and the logical address used in the initial copy process, inthe update information (step 1380; 1120 in the FIG. 11).

(9) The host CHA 110A commands the DKA 120 to write the updateinformation to the storage device 150 (in other words, it commands theDKA 120 to write the information starting from the aforementioned freshnewest update information address in the journal logical volume 230 JA),and terminates normally (step 1385; 1140 and 1160 in FIG. 11).

The foregoing was a description relating to FIG. 11 to FIG. 13. In theforegoing description, the update information is stored temporarily inthe cache memory 130, but it may also be stored temporarily in theshared memory 140, or the like.

Furthermore, the writing of the write data to the storage device 150does not have be asynchronous, in other words, it does not have to beperformed immediately after step 1360 and step 1385. If the hostcomputer 180 has implemented another write command to the logicaladdress A, then the write data in the journal is overwritten, andtherefore, before the write data is received from the host computer 180,the write data in the journal must be written to the storage device 150corresponding to logical address of the journal logical volume storingthe update information. Alternatively, it may be withdrawn to a separatecache memory, and written later to the storage device 150 correspondingto the logical address of the journal logical volume storing the updateinformation.

Moreover, in the journal creation process described above, journals aresaved in the storage device 150 (in other words, the journal logicalvolume 230 JA), but it is also possible to prepare cache memories 130 ofa prescribed size for storing the journals, in advance, and then to savethe journals to a storage device 150 when all of the cache memories havebeen used. The volume of the cache memory for the journals may also bespecified via a SVP 281, for example.

Furthermore, the read/write process 220 is a process implemented by theDKA120 in response to a command received by the DKA 120 from a CHA 110or another DKA 120. More specifically, for example, the read/writeprocess 220 is a process whereby the data in a designated cache memory130 is written to the storage region of the storage device 150corresponding to a designated logical address, or a process whereby datais read out to a designated cache memory 130, from the storage region inthe storage device 150 corresponding to a designated logical address.The read/write process 220 may, for example, be carried out by means ofthe CPU in the DKA 120 reading out a particular computer program.

FIG. 14 is a diagram for describing the operation of the host CHA 110Aof the primary storage system 100A which has received a journal readcommand (namely, for describing a journal read reception process), andFIG. 15 is a flowchart of a journal read reception process. Below, anoperation where the primary storage system 100A receives a journal readcommand from the secondary storage system 100B is described withreference to FIGS. 14 and 15. In the following description, the systemCHA 110B in the primary storage system 100A is called the “system CHA110BP” and the system CHA 110B in the secondary storage system 100B iscalled the “system CHA 110BS”.

(1) The system CHA 110BP receives an access command from the system CHA110BS. The access command contains an identifier for indicating that itis a journal read command, a group number relating to the command, andan indicator indicating the presence or absence of a retry instruction.Below the group number in the access command is taken to be group numberA (step 1220; 1410 in FIG. 14).

(2) The system CHA 110BP refers to the group information 600 andinvestigates whether or not the group status for the group number A is“normal” (step 1510). If the group status is a status other than“normal”, for instance, “problem”, in step 1510, then the system CHA110BP reports the group status to the system CHA 110BS and terminatesprocessing. The system CHA 110BS carries out processing in accordancewith the group status thus received. For example, if the group status is“problem”, then the system CHA 110BS terminates the journal read process(step 1515).

(3) If the group status of group number A is “normal” in theinvestigation in step 1510, then the system CHA 110BP investigates thestatus of the journal logical volume (step 1520). If the volume statusof the journal logical volume is not “normal” in the investigation atstep 1520, for example, if the status is “problem”, then the system CHA110BP changes the group status to “problem”, reports the changed groupstatus to the system CHA 110BS, and terminates processing. The systemCHA 110BS carries out processing in accordance with the group statusthus received. For example, if the group status is “problem”, then thesystem CHA 110BS terminates the journal read process (step 1525).

(4) If the volume status of the journal logical volume is found to be“normal” in the investigation in step 1520, then the system CHA 110BPexamines whether or not the journal read command is a retry instruction(step 1530).

(5) If the journal read command is found to be a retry instruction inthe investigation in step 1530, then the system CRA 110BP sends thepreviously transmitted journal to the secondary storage system 100B,again. The system CHA 110BP reserves the cache memory 130, and commandsthe DKA 120 to write information corresponding to the size of the updateinformation, to the cache memory, starting from the retry start addressindicated in the pointer information 700 (1420 in FIG. 14).

The read/write process 220 in the DKA 120 (for example, a computerprogram read into the CPU of the DKA 120) reads in the updateinformation from the storage device 150 (in other words, the journallogical volume 230 JA), saves this information in the cache memory 130,and reports the end of the read process to the system CHA 110BP thatoriginated the command (1430 in FIG. 14).

The system CHA 110BP receives the report indicating the end of theupdate information read process, acquires the logical address of thewrite data and the size of the write data, and then reserves a cachememory 130 and commands the DKA 120 to write the write data to thereserved cache memory 130, starting from the logical address acquired asdescribed above (step 1540; 1440 in FIG. 14).

By means of the read/write process 220, the DKA 120 reads in the writedata from the storage device 150 (more specifically, the designatedlogical address), saves the write data in the reserved cache memory 130,and reports the end of the read process to the system CHA 110BP thatoriginated the command (1450 in FIG. 14).

The system CHA 110BP receives the report indicating the end of the writedata read process, sends the update information and the write data tothe secondary storage system 100B, releases the cache memory 130 holdingthe journal, and then terminates processing (step 1545; 1460 in FIG.14).

(6) If the command is found not to be a retry instruction in theinvestigation in step 1530, then the system CHA 110BP examines whetheror not there is a journal that has not been sent, and if there is, thenit sends this journal to the secondary storage system 100B. The systemCHA 110BP compares the read start address in the pointer information 700with the newest update information address (step 1550).

If the read start address is equal to the newest update informationaddress, then this means that all of the journals have been sent to thesecondary storage system 100B, and therefore the system CHA 110BP sendsa “no journals” message to the secondary storage system 100B (step1560), and when the next journal read command is received, it releasesthe storage region of the journals that have been sent to the secondarystorage system 100B (step 1590).

In the process for releasing the journal storage region, the system CHA110BP sets the retry start address to the oldest update informationaddress in the pointer information 700. If the oldest update informationaddress has reached the head address of the write data region, then thesystem CHA 110BP sets the oldest update information address to zero. Thesystem CHA 110BP changes the oldest write data address in the pointerinformation 700 to the existing value plus the size of the write datasent in accordance with the previous read journal command. If the oldestwrite data address has reached a logical address equal to or exceedingthe capacity of the journal logical volume, then the system CHA 110BPcorrects the address by subtracting the head address of the write dataregion.

(7) If, at step 1550, there is a journal that has not been sent, thenthe system CHA 110BP reserves a cache memory 130, and commands the DKA120 to write the update information to the cache memory 130 thusreserved, from the read start address in the pointer information 700 (inother words, to read out information of the prescribed size, from theread start address) (1420 in FIG. 14).

By carrying out a read/write process 220 in response to this command,the DKA 120 reads in the update information from the storage device 150(in other words, the journal logical volume 230 JA), saves thisinformation in the cache memory 130, and reports the end of the readprocess to the system CHA 110BP that originated the command (1430 inFIG. 14).

The system CHA 110BP receives the report indicating the end of theupdate information read process, acquires the logical address of thewrite data and the size of the write data, from the update informationread out, and then reserves a cache memory 130 and commands the DKA 120to read in write data of the acquired data size, from the acquiredlogical address to the reserved cache memory 130 (step 1570; 1440 inFIG. 14).

By means of the read/write process 220, the DKA 120 reads in the writedata from the storage device 150 (more specifically, the designatedlogical address of the journal logical volume 230JA) in accordance withthis command, saves the write data in the reserved cache memory 130, andreports the end of the read process to the system CHA 110BP (1450 inFIG. 14).

The system CHA 110BP receives the report indicating the end of the writedata read process, sends the update information and the write data tothe secondary storage system 100B (step 1580), and releases the cachememory 130 holding the journal (1460 in FIG. 14). The system CHA 110BPthen sets the read start address as the retry start address in thepointer information 700, and sets a value obtained by adding the readstart address to the update information size of the transmitted journal,as the new read start address in the pointer information 700.

(8) When the previous journal read command has been processed, thesystem CHA 110BP releases the storage region of the journals that havebeen sent to the secondary storage system 100B (step 1590).

The foregoing was a description relating to FIG. 14 to FIG. 15. In thejournal read reception process described above, the primary storagesystem 100A transmitted the journals to the secondary storage system100B, one at a time, but it is also possible to send a plurality ofjournals to the secondary storage system 100B, simultaneously. Thenumber of journals that can be sent by means of one journal read commandmay be specified by the secondary storage system 100B in the journalread command, or it may be specified to the primary storage system 100Aor the secondary storage system 100B by the user at a prescribed time,for instance, when the group is registered. Moreover, it is alsopossible for the primary storage system 100A or the secondary storagesystem 100B to change the number of journals sent by a single journalread command in a dynamic fashion, depending on the transmissioncapacity, load, or the like, of the connection path 200 between theprimary storage system 100A and the secondary storage system 100B.Furthermore, the journal transfer volume may be specified, rather thanthe number of journals, by taking account of the size of the write datain the journals. This transfer volume may also be changed dynamically.

Furthermore, in the journal read reception process described above, thejournals are read in from the storage device 150 to the cache memory130, but if they are situated in the cache memory 130, then theaforementioned processing does not have to be carried out.

Moreover, the process for releasing the storage region of the journal inthe journal read reception process was described as being implementedwhen the next journal read command is processed, but it may also beimplemented immediately after the journals have been sent to thesecondary storage system 100B. Furthermore, the secondary storage system100B may establish an update number at which the storage region may bereleased in the journal read command, the primary storage system 100Areleasing the journal storage region in accordance with thisinstruction.

FIG. 16 illustrates the sequence of a journal read command process 240,and FIG. 17 is a flowchart of a journal read command process 240. FIG.18 is a flowchart of a journal storage process. Below, an operation isdescribed wherein the system CHA 110BS of the secondary storage system100B reads out a journal from the primary storage system 100A, andstores that journal in a journal logical volume in the secondary storagesystem 100B (hereinafter, called the “journal logical volume 230 JB”).Furthermore, in FIG. 16, the journal read command process 240 isreferred to as “JNLRD process 240”).

(1) The system CHA 110BS reserves the cache memory 130 for storing thejournal, generates an access command containing an identifier indicatingthat it is a journal read command, the group number in the primarystorage system 100A relating to that command, and an indicator showingwhether or not it is a retry instruction. The system CHA 110BS sendsthis access command to the primary storage system 100A. Below, the groupnumber in the access command is taken to be group number A (step 1700;1610 in FIG. 16). The group number A can be acquired, for example, bymeans of the system CHA 110BS referring to the group information 600,path information 500, or the like, held in the secondary storage system100B, identifying the primary logical volume number corresponding to thesecondary logical volume number contained in the group number to whichthe journal logical volume 230JB belongs, and then making an inquiry tothe primary storage system 100A with regard to the group number to whichthe identified primary logical volume number belongs.

(2) The system CHA 110BS receives a response and a journal from theprimary storage system 100A (1620 in FIG. 16). The system CHA 110BSexamines the response thus received, and if the response is “nojournals”, then this means that there are no journals in the group ofthe primary storage system 100A corresponding to the designated groupnumber A. Therefore, after a prescribed time period has elapsed, thesystem CHA 110BS sends a read journal command to the primary storagesystem 100A (steps 1720 and 1725).

(4) If the response of the primary storage system 100A is “group statusindicates abnormal” or “group status indicates unused”, then the systemCHA 110BS changes the group status in the secondary storage system 100B(the group status of the group to which the journal logical volume 230JBbelongs) to the status thus received, and it then terminates the journalread process (steps 1730 and 1735).

(5) If the response of the primary storage system 100A is any responseother than the above, in other words, if it indicates normaltermination, then the system CHA 110BS refers to the volume information400 and investigates the volume status of the journal logical volume230JB (step 1740). If the volume status of the journal logical volume230JB is “abnormal”, then this means that the journal cannot be storedin the journal logical volume 230JB, and therefore the system CHA 110BSchanges the group status corresponding to the group to which the journallogical volume 230JB belongs, to “abnormal”, and it then terminates theprocess (step 1745). In this case, the system CHA 110BS may carry outprocessing for changing the journal logical volume to a normal logicalvolume, for example, and it may return the group status to “normal”.

(6) If the volume status of the journal logical volume is found to be“normal” in the investigation in step 1740, then the system CHA 110BScarries out journal storage processing 1800 as described below. If thejournal storage process 1800 terminates normally, then the system CHA110BS sends the next journal read command (step 1760). Instead of this,it is also possible for the system CHA 110BS to generate and send thenext journal read command, when a certain time period has elapsed afternormal termination of the journal storage process 1800. The system CHA110BS may send subsequent journal commands in a periodic fashion, atprescribed time intervals, or alternatively, it may determine the timingfor sending the next journal command on the basis of the number ofjournals received, the transmission volume in the connection path 200,and the storage capacity of the journal logical volume held in thesecondary storage system 100B, or the load on the secondary storagesystem 100B, or the like, or on the basis of the journal storagecapacity held by the primary storage system 100A (or the pointerinformation 700 of the primary storage system 100A), acquired from theprimary storage system 100A. The aforementioned transfer of informationmay be implemented by means of a special command, or it may be includedin a response to the journal read command. Subsequent processing is thesame as that from step 1710 onwards.

(7) If the journal storage process at step 1800 does not terminatenormally, then this means that there is insufficient free space in thejournal logical volume, and therefore the system CHA 110BS discards thereceived journal, and sends a journal read command indicating a retryinstruction, when a prescribed time period has elapsed (step 1755).Alternatively, the system CHA 110BS may retain the journal in a cachememory 230 and carry out journal storage processing again, when aprescribed time period has elapsed. This is because there is apossibility that the unused space in the journal logical volume willhave increased when the prescribed time period has elapsed, due to arestore process 250 (described hereinafter) having been implemented. Inthe case of this method, an indicator showing whether or not the commandis a retry instruction does not have to be included in the journal readcommand.

Next, the journal storage process 1800 illustrated in FIG. 18 will bedescribed.

(1) The system CHA 110BS investigates whether or not a journal can bestored in the journal logical volume 230JB. More specifically, using thepointer information 700 held in the secondary storage system 100B, thesystem CHA 110BS investigates whether or not there is unused space inthe update information region (step 1810). If the newest updateinformation address and the oldest update information address in thepointer information 700 are equal, then this means that there is nounused space in the update information region, and therefore the systemCHA 110BS terminates the process as “failed to create journal” (step1820).

(2) If, in the investigation in step 1810, there is unused space in theupdate information region, then the system CHA 110BS examines whether ornot it is possible to store write data in the write data region, on thebasis of the pointer information 700 (step 1830). If the sum of thenewest write data address and the data volume of the write data is equalto or greater than the oldest write data address, then this means thatthe write data cannot be stored in the write data region, and thereforethe system CHA 110BS terminates the process as “failed to createjournal” (step 1820).

(3) If the journal can be stored, then the system CHA 110BS changes thegroup number contained in the update information of the journal receivedby means of the journal read process 240, and the logical address forthe write data in the journal logical volume (hereinafter, called the“journal write data address”). More specifically, the system CHA 110BSchanges the group number in the update information to the group numberof the secondary storage system 100B (the group number of the group towhich the journal logical volume 230JB belongs), and it changes thejournal write data address in the update information to the newest writedata address in the pointer information 700 provided by the secondarystorage system 100B. The system CHA 110BS changes the newest updateinformation address in the pointer information 700 to the value of theexisting newest update information address plus the size of the updateinformation. The system CHA 110BS also changes the newest write dataaddress in the pointer information 700 to the value of the existingnewest write data address plus the size of the write data (step 1840).

(4) The system CHA 110BS reserves the cache memory 130, stores theupdate information and the write data in the reserved cache memory 130,commands the DKA 120 to write the update information and the write datato a storage device 150 (in other words, to the journal logical volume230JB), and then terminates the process as “journal createdsuccessfully” (step 1850; 1630 in FIG. 16). Thereupon, by means of theread/write process 220, the DKA 120 writes the update information storedin the cache memory 130 and the write data to the storage device 150,and it then releases the cache memory 130 that was reserved 1640 in FIG.16).

Moreover, in the journal storage process described above, journals aresaved in the storage device 150, but it is also possible to preparecache memories 130 of a prescribed size for storing the journals, inadvance, and then to save the journals to a storage device 150, from allof the cache memories, when all of the cache memories have been used.The cache memory volume used for the journals may also be specified viaa SVP 281, for example.

FIG. 19 is a diagram for describing a restore process 250, and FIG. 20is a flowchart of this restore process 250. Below, an operation whereinthe host CHA 110A of the secondary storage system 100B updates data byusing a journal is described with reference to FIG. 19 and FIG. 20. Therestore process 250 may be performed by a separate CHA 110 (for example,the system CHA 110BS), or it may be performed by the DKA 120 of thesecondary storage system 100B.

(1) The host CHA 110A refers to the group information 600 andinvestigates whether or not the group status of the group numberselected from a plurality of group numbers is “normal” (step 2010). Ifthe group status is found to be a status other than “normal”, forexample, “problem”, in the investigation at step 2010, then the host CHA110A ends the restore process 250 (step 2015).

(2) If the group status is found to be “normal” in step 2010, then thehost CHA 110A refers to the group information 600, the volumeinformation 400, and the like, and examines the volume statuscorresponding to the journal logical volume number belonging to theselected group number (step 2020). If the volume status of the journallogical volume 230JB is found to be “abnormal” in the investigation instep 2020, then this means that that logical volume cannot be accessed,and therefore the host CHA 110A changes the group status correspondingto the selected group number to “abnormal” and terminates processing(step 2025).

(3) If the volume status of the journal logical volume 230JB is found tobe “normal” at step 2020, then the host CHA 110A investigates whether ornot there exists a journal that is to be restored. More specifically,the host CHA 110A acquires the oldest update information address and thenewest update information address in the pointer information 700, and itcompares these addresses. If the oldest update information address andthe newest update information address are equal, then this means that nojournal is present, and hence the host CHA 110A temporarily ends therestore process, and once a prescribed period of time has elapsed, itrestarts the restore process (step 2030).

(4) If there is a journal to be restored, as a result of theinvestigation in step 2030, then the host CHA 110A carries out thefollowing processing with respect to the journal having the oldest(smallest) update number. The update information in the journal havingthe oldest (smallest) update number is saved, starting from the oldestupdate information address indicated in the pointer information 700. Thehost CHA 110A reserves a cache memory 130 and commands the DKA 120 toread information corresponding to the update information size (in otherwords, the update information itself), from the oldest updateinformation address to the cache memory 130 (1910 in FIG. 19).

The read/write process 220 performed by the DKA 120 involves reading theupdate information from the storage device 150 (in other words, thejournal logical volume 230JB), saving that update information to thereserved cache memory 130, and then reporting completion of the readoperation to the host CHA 110 (1920 in FIG. 19).

The host CHA 110A receives the report indicating completion of theupdate information read process, acquires the logical address of thewrite data and the size of the write data, and then reserves a cachememory 130 and commands the DKA 120 to read data corresponding that datasize (in other words, one item of write data), from the acquired logicaladdress to the cache memory 130 (1930 in FIG. 19).

The read/write process 220 performed by the DKA 120 involves reading thewrite data from the storage device 150 (in other words, from thedesignated logical address), saving that write data to the cache memory130, and then reporting completion of the read operation to the host CHA110 (step 2040; 1940 in FIG. 19).

(5) The host CHA 110A determines the logical address of the secondarylogical volume to be updated (in other words, the logical address of thewrite command (see FIG. 21)), from the update information, and commandsthe DKA 120 to write the write data to the address of the secondarylogical volume 230 SB identified by that logical address (step 2050;1950 in FIG. 19). The read/write process 220 performed by the DKA 120involves writing the write data stored in the cache memory 130, to thestorage region of the storage device 150 corresponding to the logicaladdress in the secondary logical volume (the logical address of thewrite command), and then releasing the cache memory 130 and reportingcompletion of the write operation to the host CHA 110A (1960 in FIG.19).

(6) The host CHA 110A receives the write process completion report andreleases the journal storage region. In the process for releasing thejournal storage region, the host CHA 110A changes the oldest updateinformation address in the pointer information 700 provided in thesecondary storage system 100B, to a value equal to the current oldestupdate information address plus the update information size. If theoldest update information address has reached the head address of thewrite data region, the host CHA 110A sets the head address of the writedata region to 0. The host CHA 110A changes the oldest write dataaddress in the pointer information 700 to a value equal to the existingoldest write data address plus the size of the write data that has beenwritten. If the oldest write data address has reached a logical addressequal to or exceeding the capacity of the journal logical volume, thenthe host CHA 110A corrects the address by subtracting the head addressof the write data region. Thereupon, the host CHA 110A starts the nextrestore process (step 2060).

The foregoing was a description relating to FIG. 19 to FIG. 20.Furthermore, in the restore process 250 described above, the journalsare read in from the storage device 150 to the cache memory 130, but ifthey are situated in the cache memory 130, then the aforementionedprocessing does not have to be carried out.

Furthermore, in the journal read reception process and the journal readcommand process 240 described above, the journal to be sent isdetermined by the primary storage system 100A in accordance with thepointer information 700, but the journal to be sent may also bedetermined by the secondary storage system 100B. For example, the systemCHA 110BS adds an update number to the journal read command. In thiscase, in order that the system CHA 110BP receiving the journal readcommand may determine the logical address of the update informationhaving the update number designated by the secondary storage system100B, in the journal read reception process, a table or index may beprovided in the shared memory 140 of the primary storage system 100A,for determining the logical address at which the update information isstored on the basis of the update number.

Furthermore, in the journal read reception process and the journal readcommand process 240 described above, a journal read command was used,but it is also possible to use a normal read command. For example, thegroup information 600 and the pointer information 700 in the primarystorage system 100A may be transferred previously to the secondarystorage system 100B, and the secondary storage system 100B may then readthe data in the journal logical volume of the primary storage system100A (in other words, the journal).

Furthermore, in the journal read reception process described above, thejournals are sent from the primary storage system 100A to the secondarystorage system 100B in the order of their update numbers, but they donot have to be sent in update number order. Furthermore, it is alsopossible for a plurality of journal read commands to be send from theprimary storage system 100A to the secondary storage system 100B. Inthis case, in order to process the journals in update number order inthe restore process, a table or index may be provided in the secondarystorage system 100B in such a manner that the logical address at whichthe update information is stored can be determined from the updatenumber.

In the data processing system 1 described above, the primary storagesystem 100A generates journals and transmits these journals to thesecondary storage system 100B, and the secondary storage system 100Breplicates data on the basis of the journals it receives from theprimary storage system 100A. In this way, no burden is placed on thehost computer 180 connected to the primary storage system 100A by thedata replication process, and hence the connection path 190 between theprimary storage system 100A and the host computer 180 does not have tobe used.

The foregoing was a description of a mode of implementation relating tobasic data processing using journals. Below, several embodimentsrelating to the application of data processing using journals will bedescribed.

Embodiment 1

FIG. 23 shows an overview of a compositional example of a dataprocessing system relating to a first embodiment of one mode ofimplementing the present invention. The following description focusesprincipally on the points of difference with respect to theaforementioned mode of implementation, and points which are common withthe aforementioned mode of implementation are explained briefly oromitted from this description. Moreover, in the following description,the reference numeral 101A is appended to the control sub-system of theprimary storage system 100A, and the reference numeral 101B is appendedto that of the secondary storage system 100B. Moreover, the volumeinformation, path information, group information and pointer informationprovided in the primary storage system 100A contain information relatingto the primary storage system 100A, and are appended with the suffix A.At least one of the volume information 400A, the path information 500A,the group information 600A and the pointer information 700A may belocated in the control sub-system 101B, and similarly, at least one ofthe volume information 400B, path information 500B, group information600B and pointer information 700B may be located in the controlsub-system 101A. Moreover, in this case, if one of the informationelements is updated (for example, the path information 500A), then theupdated contents may be reflected in the same information (for example,path information 500A) held in the other control sub-system, by means ofthe connection path 200. Moreover, the volume information, pathinformation, group information and pointer information provided in thesecondary storage system 100B contain information relating to thesecondary storage system 100B, and are appended with the suffix B. InFIG. 23, the “#” symbol in a logical volume indicates the logical volumenumber. Moreover, the reference symbol “P” is appended to the primarylogical volume (shown as “P-VOL”), the reference symbol “S” is appendedto the secondary logical volume (shown as “S-VOL”), the reference symbol“A” is appended to the journal logical volumes in the primary storagesystem 100A (shown as “JNLVOL”), and the reference symbol “B” isappended to the journal logical volumes in the secondary storage system100B. Below, when referring to a logical volume, in order to make thedescription easier to understand, a combination of the # appended to thelogical volume and the aforementioned reference symbol will be used,instead of reference numbers such as “230”.

A plurality of journal logical volumes, for example, three journallogical volumes, #1A, #2A and #3A are included in a particular group102A of the plurality of groups established in the primary storagesystem 100A. Furthermore, the group 102 also contains one primarylogical volume, #4P, for example, which is a logical volume wherejournals are not stored and only write data is stored.

A plurality of journal logical volumes, for example, three journallogical volumes, #1B, #2B and #3B are included in a particular group102B of the plurality of groups established in the secondary storagesystem 100B. Furthermore, the group 102 also contains one secondarylogical volume, #4S, for example, which is a logical volume wherejournals are not stored and only write data is stored. In order to makethe contents of the present embodiment easier to understand, the numberof journal logical volumes contained in group 102A and the number ofjournal logical volumes contained in group 102B are taken to be thesame, but these numbers may be different. Moreover, the respectivestorage capacities of the journal logical volumes #1A, #2A and #3A mayalso be different. The same applies to the journal logical volumes #1B,#2B and #3B.

If the control sub-system 101A has received a write command and writedata for the primary logical volume #4P, from the host computer 180,then it stores the write data in the primary logical volume #4P inaccordance with that write command. Moreover, the control sub-system101A refers to the group information 600, ascertains the update numbercorresponding to the group number of the group 102A (hereinafter, alsoreferred to as the “SEQ#”), and generates a journal containing theupdate number thus ascertained, and the like. The control sub-system101A selects a first journal logical volume forming a storagedestination for the update information in the journal, and a secondjournal logical volume forming a storage destination for the write datain the journal, from the plurality of journal logical volumes #1A, #2Aand #3A. It stores the update information contained in the generatedjournal in the first journal logical volume thus selected, and it storesthe write data contained in the generated journal, in the second journallogical volume thus selected. A more concrete description is givenbelow.

FIG. 24 shows an example of the composition of the pointer information700A in the first embodiment of one mode of implementing the presentinvention. FIG. 25 shows the composition of the pointer information 700Aillustrated in FIG. 24, and this information is constituted in aplurality of journal logical volumes #1A, #2A, #3A. Below, thecomposition of the pointer information 700A in the primary storagesystem 100A and the plurality of journal logical volumes #1A, #2A and#3A are described with reference to FIG. 24 and FIG. 25, but thisdescription can also be applied to the secondary storage system 100B.

Of the plurality of information elements in the pointer information700A, the head address of the update information region, the headaddress of the write data region, the newest write data address and theoldest write data address are registered for each of the journal logicalvolumes located in the corresponding group.

According to the example in FIG. 24 and FIG. 25, the update informationand the write data constituting the same journal are stored in aseparate journal logical volume. More specifically, it is possible tostore the update information and the write data respectively by means ofthe following methods, for example.

(Method for Storing Update Information in the Journal)

The control sub-system 101A selects a journal logical volume from theplurality of journal logical volumes, for example, the journal logicalvolume #1A having the most recent number, stores the update information310 starting from the head position of the selected journal logicalvolume #1A, and then proceeds to update the information elementscorresponding to journal logical volume #1 which are contained in thepointer information 700A, each time an update arises. Consequently, ifthe control sub-system 101A detects that the selected journal logicalvolume #1A has been used to the end of the update information region(the head address of the write data region), it selects a separatejournal logical volume, for example, the journal logical volume #2Ahaving the next most recent number, and stores the update information310 from the head position of the selected journal logical volume #2A.Thereafter, similarly, if the storage region up to the end of the updateinformation region (the head address of the write data region) in thejournal logical volume #2 has been used, then the control sub-system101A selects another journal logical volume, for example, the journallogical volume #3 and stores the update information 310 starting fromthe head position of this journal logical volume. If the storage regionhas been used up to the end of the update information region of journallogical volume #3 (up to the head address of the write data region), andthere is no other unused journal logical volume, then the controlsub-system 101A stores the update information 310 starting from the headposition of the initially selected journal logical volume #1A. Instoring the update information, the plurality of journal logical volumesmay be selected in accordance with a previously determined sequence (forexample, a sequence established in the shared memory 260, or the like),or it may be selected in a random manner. Furthermore, similarly to themethod for storing write data described below, first and second updateinformation having adjacent update numbers (for example, havingconsecutive update numbers) may be divided between separate journallogical volumes rather than being stored in the same journal logicalvolume.

(Method for Storing Write Data in the Journal)

The control sub-system 101A changes the journal logical volume formingthe storage destination for the write data, for each journal. Morespecifically, for example, if there are N journal logical volumes (forexample, 3 journal logical volumes) in the group 102A, the controlsub-system 101A divides the update number in the update informationforming a pair with the write data that is to be stored (for example,5), by N (for example, 3), and stores the write data that is to bestored in the journal logical volume corresponding to the remaindervalue (for example, 2), namely, journal logical volume #2A. The storagedestination address for the write data in the journal logical volume(for example, #2A) forms the newest write data address corresponding tothat journal logical volume in the pointer information 700A. The firstand second write data having adjacent update numbers are not necessarilystored in the same journal logical volume, but according torequirements, they may be stored in the same journal logical volume (forexample, if the write data regions of the other journal logical volumesare full). Moreover, similarly to the update information storage methoddescribed above, the first and second write data having adjacent updatenumbers may be stored in the same journal logical volume, and if thisjournal logical volume becomes full, then they may be stored in anotherjournal logical volume.

The foregoing description related to a method for storing the updateinformation and the write data in the journal. If this storage method isadopted, the following processing can be carried out in the journalcreation process (for example, step 1345 in FIG. 13 and step 1830 inFIG. 18) described in the aforementioned mode of implementation, forexample.

The control sub-system 101A selects the journal logical volume formingthe storage destination for the write data, from a plurality of journallogical volumes, and judges whether or not write data can be stored inthat logical volume, on the basis of the various information elementscorresponding to the selected journal logical volume (the informationelements registered in the pointer information 100A). More specifically,for example, the control sub-system 101A divides the update number inthe update information forming a pair with the write data that is to bestored (for example, 5), by the number of journal logical volumes Nexisting in group 102A (for example, 3), and it judges whether or notthe write data can be stored in the journal logical volume correspondingto the remainder of this division operation (for example, 2), (namely,the journal logical volume #2A). If a negative judgment result isobtained, then the control sub-system 101A terminates the process as“failed to create journal” (step 1390 in FIG. 13, and step 1830 in FIG.18). Rather than terminating the process, the control sub-system 101Amay also search for a journal logical volume having sufficient freespace to store the write data, on the basis of the data size of thewrite data and the pointer information 700A, and the like, and thenstore the write data in the free space of the journal logical volumefound by this search.

According to the first embodiment described above, a plurality ofjournal logical volumes are prepared for one group, and a first and asecond write data having adjacent update numbers (for example,consecutive update numbers) are stored in separate journal logicalvolumes. Thereby, it is possible to make the writing of the write dataoverlap with the reading of the journal (in a “pipeline” fashion), andhence copying performance is improved. More specifically, if there isone journal logical volume, then the read (or write) performance for thewrite data is dependent on the performance of the storage device 150providing that journal logical volume. In the present embodiment, aplurality of journal logical volumes are prepared and the write data injournals having adjacent update numbers is stored in different journallogical volumes. Therefore, it is possible to use a plurality of storagedevices 150 simultaneously, and hence the journal read (or write)performance can be enhanced. In order to achieve such improvedperformance in a satisfactory manner, it is desirable that the pluralityof journal logical volumes are provided in separate storage devices 150.Furthermore, if each journal logical volume is provided over a pluralityof storage devices 150, then when providing a plurality of journallogical volumes, it is desirable that all or a part of the plurality ofstorage devices 150 providing one journal logical volume do not overlapwith all or a part of the plurality of storage devices 150 providinganother journal logical volume.

In the first embodiment described above, after step 1580 in FIG. 15 andbefore receiving a journal read command from the secondary storagesystem 100B, the control sub-system 101A may implement a read processautonomously in order to read one or more subsequent journals (in otherwords, the journal having the next update number onwards, in thejournals sent at step 1580). Thereby, when the next journal read commandis received, in the read process in step 1570 there will be an increasedpossibility that the journal corresponding to that command will alreadybe situated in the cache memory 130, and therefore the time fromreceiving the journal read command until sending a journal to thesecondary storage system 100B in accordance with that command can bereduced. Here “one or more subsequent journals” can be taken to meanjournals up to the update number equal to the sum of previous updatedata plus the number of journal logical volumes, n, for example. In thiscase, in the secondary storage system 100B, the write data in thejournal is stored continuously in the same journal logical volume.

Moreover, in the first embodiment, as described above, the first andsecond update information having adjacent update numbers (for example,consecutive update numbers), may be stored in separate journal logicalvolumes, similarly to the method for storing the write data.

Moreover, in this first embodiment, the plurality of journal logicalvolumes belonging to the same group do not have to have the same storagecapacity.

Furthermore, in the first embodiment, it is also possible to implementthe following, as a modification example.

(A) First Modification of First Embodiment

The control sub-system 101B of the secondary storage system 100Bsuperimposes m journal read commands (where m is an integer of 2 orabove) and it sends the m superimposed journal read commands to theprimary storage system 100A. The control sub-system 101B inserts anumber (hereinafter, called a “TAG#”) for identifying the journal readcommand in each of the m superimposed journal read commands. TheTAG#ranges from 1 to m. More specifically, for example, if there arethree superimposed journal read commands, then the control sub-system101B inserts a TAG#1 into the first journal read command of the threesuperimposed journal read commands, inserts a TAG#2 in the secondjournal read command, inserts a TAG#3 in the third journal read command,and then sends the three superimposed journal read commands to theprimary storage system 100A. In this case, in the primary storage system100A, as illustrated in FIG. 26, specific information elements in thepointer information 700A (for example, the read start address and theretry start address) are provided in equal number to the number ofsuperimposed commands, m, in other words, they are provided for eachTAG#. The number of superimposed commands, m, may be the same as thenumber of journal logical volumes provided in the group 102A, forexample. Furthermore, according to the pointer information 700Aillustrated in FIG. 26, if the write data is read out from the journallogical volume #1A corresponding to TAG#1, then the read start addressand the retry start address corresponding to the TAG#1 are the address“150” from the head position in logical volume number “1”.

A more concrete description of this first modification example is givenbelow.

The control sub-system 101B of the secondary storage system 100Bimplements the journal read command processing illustrated in FIG. 17for each TAG#.

When the control sub-system 101A of the primary storage system 100A hasreceived a journal read command, it implements the journal receptionprocessing described with reference to FIG. 15. In the journal receptionprocess, the control sub-system 101A reads out the update information310 from the logical address indicated by the retry start address andthe read start address corresponding to the TAG#(the informationelements included in the pointer information 700A) (steps 1570 and1540). By means of the journal reception process, a journal containingupdate information is sent to the secondary storage system 100B. In thiscase, in order to identify the journal read command on the basis ofwhich the journal was acquired, the control sub-system 101A appends theTAG# in the corresponding journal read command to the acquired journaland sends the journal with the appended TAG# to the secondary storagesystem 100B.

If the control sub-system 101B of the secondary storage system 100Breceives a journal, then it implements the journal storage processingdescribed with reference to FIG. 18. In this case, the controlsub-system 101B calculates the logical address for storing the updateinformation in the journal, on the basis of the TAG# and update numberin the received journal and the pointer information 700B, andinvestigates whether or not update information can be stored in thejournal logical volume identified by the TAG#, on the basis of thecalculated logical address and the size of the update information (step1810 in FIG. 18). Furthermore, the control sub-system 101B investigateswhether or not write data can be stored in the identified journallogical volume, on the basis of the data size of the write data in theupdate information, and the pointer information 700B (step 1830 in FIG.18). The journal logical volume where the update information and thewrite data are stored is the journal logical volume corresponding to theTAG#.

In this way, even greater copy performance can be achieved by sendingjournal read commands in a superimposed fashion.

(A) Second Modification of First Embodiment

The second modification is a further modification of the firstmodification example, wherein the primary storage system 100A acquires aplurality of journals and sends them to the secondary storage system100B, in response to one journal read command. A more concretedescription is given below.

In the journal reception process described with respect to FIG. 15, thecontrol sub-system 101A of the primary storage system 100A acquires andsends the write data stored in consecutive storage regions of the samejournal logical volume. More specifically, for example, in FIG. 25, thecontrol sub-system 101A ascertains from the pointer information 700A,and the like, that the two write data registered in consecutive regionsof the journal logical volume #1A correspond respectively to updatenumber 1 and update number 4. Thereby, it generates update informationincluding the update number 1 and a journal containing write datacorresponding to same, and update information including the updatenumber 4 and a journal containing write data corresponding to same, inresponse to one journal read command, and transmits them to thesecondary storage system 100B. After the processing in step 1590 (or1545) in FIG. 15, the control sub-system 101A determines the logicaladdress for storing the two or more update information containedrespectively in the two or more journals that are to be generatedsubsequently. In this case, the logical address is equal to the readstart address plus the value obtained by multiplying the number of TAG#,m, by the update information sizes.

The control sub-system 101B of the secondary storage system 100B havingreceived the journals implements the journal storage processingdescribed with respect to FIG. 18, but in this case, the write data inthe received journal is stored from the newest write data address in thejournal logical volume corresponding to the TAG#appended to the receivedjournal. In the example in FIG. 25, if the control sub-system 101B hasreceived two journals having update number 1 and update number 4, thenit writes the write data in the journal having update number 1 to thejournal logical volume #1, starting from the logical address 700, and itthen stores the write data in the journal having update number 4, in acontinuous fashion following this write data.

Embodiment 2

Next, a second embodiment of one mode of implementing the presentinvention will be described. The second embodiment is further example ofapplication of the first embodiment described above. The followingdescription focuses principally on the points of difference with respectto the aforementioned first embodiment, and points which are common withthe aforementioned first embodiment are explained briefly or omitted.

In the second embodiment, the write data region in the journal logicalvolume is divided into a plurality of sub write regions. The pluralityof sub write regions may respectively have the same storage capacity orthey may have different storage capacities. In this second embodiment,they each have the same storage capacity. In other words, in the secondembodiment, the write data region in the journal logical volume isdivided equally into a plurality of sub write regions. Hereinafter, theindividual sub write regions are called “extents”.

FIG. 27 shows an example of the composition of a plurality of journallogical volumes, #1A, #2A, #3A. FIG. 28 shows an example of thecomposition of extent information for managing a plurality of extents.FIG. 29 shows an example of the composition of pointer information 700Acorresponding to FIG. 27 and FIG. 28. Below, a plurality of journallogical volumes #1A, #2A and #3A in the primary storage system 100A, theextent information 701 and the pointer information 700A are describedwith reference to FIG. 27 to FIG. 29, but this description can also beapplied to the secondary storage system 100B.

As shown in FIG. 27, the write data region in the plurality of journallogical volumes #1A, #2A and #3A is divided equally into a plurality ofextents (for example, four extents). An extent number for identifyingthe extent in the journal logical volume (for example, #0-#3) isappended to each of the extents in each of the journal logical volumes.

Moreover, as shown in FIG. 27, the write data regions of all of thejournal logical volumes are also divided respectively into a pluralityof extents, in a similar fashion. In other words, each of the journallogical volumes #1A, #2A and #3A has a write data region of the samestorage size and containing the same number of extents. Therefore, atleast the plurality of write data regions of the plurality of journallogical volumes #1A, #2A and #3A are each of the same size (theplurality of update information regions may each be of the same size, orof different sizes).

Furthermore, as shown in FIG. 27, the same extent number is not usedtwice in each individual journal logical volume, but in the plurality ofjournal logical volumes #1A, #2A and #3A (in other words, within thesame group 102A), common extent numbers are used. More specifically, ineach of the journal logical volumes #1A, #2A and #3A, there are fourextents respectively labeled with the extent numbers, #0-#4. In otherwords, each write data region of each journal logical volume is dividedinto a plurality of sub write regions, and one extent is constituted byeach sub write region of the plurality of journal logical volumes.Stated alternatively, by specifying one extent number (for example, #0),one sub write region is identified in each of the plurality of journallogical volumes #1A, #2A and #3A, and the set of identified sub writeregions forms one extent corresponding to the specified extent number.Stated in yet another way, each extent extends over a plurality oflogical volumes #1A-#3A belonging to the same group 102A.

An example of the composition of the extent information 701 for managingextents of this kind is illustrated in FIG. 28.

More specifically, the extent information 701 registers, for each extent#, which of the plurality of journal logical volumes #1A-#1C the extentcorresponding to that extent # is located in. The location of the extentis indicated by a set comprising the start logical address and the endaddress, and such sets exist in equal number to the number of journallogical volumes #1A-#1C belonging to the same group 102A. The startlogical address indicates the logical address at which storage of thewrite data starts, and end logical address indicates the logical addressat which storage of the write data ends. Furthermore, in the extentinformation 701, the numbers #1-#3 registered respectively against theplurality of sets of start logical address and end logical addressindicate the storage order of the write data.

It is possible to ascertain the following, for example, from the extentinformation 701 of this kind.

It can be seen that in the extent having the extent #0, initially,storage of write data starts from the address 700 in journal logicalvolume #1A, and if write data has been stored up to the position ofaddress 1119 in volume #1A, then storage of write data subsequentlystarts from the position of address 700 in journal logical volume #2A.If the write data has been stored up to the position of address 1119 injournal logical volume #2A, then subsequently, storage of storage deviceis started from the position of address 700 in journal logical volume#3A.

It can be seen that in the extent having the extent #2, initially,storage of write data starts from the address 1200 in journal logicalvolume #2A, and if write data has been stored up to the position ofaddress 1699 in volume 2A, then storage of write data subsequentlystarts from the position of address 1200 in journal logical volume #23A.

In this way, by changing the journal logical volume at which the storageof the write data starts initially, for each extent #, it is possible tocause all of the journal logical volumes #1A-#3A to function inparallel.

If write data is to be stored in the respective journal logical volumes#1A-3A on the basis of the extent information 701 described above, thenthe pointer information 700A will have the composition illustrated inFIG. 29. In other words, the head address of the update informationregion and the head address of the write data region are prepared foreach journal logical volume #, and the newest write data address, theoldest write data address, the read start address and the retry startaddress are prepared for each extent #. By adjusting the newest writedata address, the oldest write data address, the read start address andthe retry start address, it is possible to write a plurality of writedata having adjacent (for example, consecutive) update numbers, inseparate extents.

In this second embodiment, the method for storing the update informationis the same as that of the first embodiment, but the method for storingwrite data is different.

For example, for each journal, the control sub-system 101A changes theextent where the write data in that journal is stored. Morespecifically, if there are n extents (where n=4, for instance), then thecontrol sub-system 101A divides the update number in the journal (forexample, 12) by the number of extents (for example, 4), and stores thewrite data contained in the journal in the extent corresponding to theremainder of this division operations (for example, 0) (namely, extent#0). The storage destination address in that extent is the newest writedata address corresponding to the number of the extent (the newest writedata address registered in the pointer information 700A). The controlsub-system 101A is able to detect whether the storage destinationaddress has reached the end address (for example, address 1200) of onepart of a certain extent (for example, #0) provided in a certain journallogical volume (for example, #1A), on the basis of the pointerinformation 700A and the extent information 701. Furthermore, in thiscase, the control sub-system 100A uses the extent information 701 tolocate the start address of another part of the same extent provided inanother journal logical volume that is to be set as the next storagedestination address (for example, it determines that the address 700 ofthe journal logical volume #2A is to be the next storage destinationaddress). The control sub-system 101A is then able to set this storagedestination address as the newest write data address and store writedata from that start address.

If this write data storage method is adopted, the following processingcan be carried out in the journal creation process (for example, step1345 in FIG. 13 and step 1830 in FIG. 18) described in theaforementioned mode of implementation, for example.

The control sub-system 101A divides the update number in the journal(for example, 12) by the number of extents, n, (for example, 4), andjudges whether or not it is possible to store the write data containedin the journal, in the extent corresponding to the remainder of thedivision operation (for example, 0), (namely, the extent #0). If anegative judgment result is obtained, then the control sub-system 101Aterminates the process as “failed to create journal” (step 1390 in FIG.13, and step 1830 in FIG. 18). Rather than terminating the process, thecontrol sub-system 101A may also search for a further extent havingsufficient free space to store the write data, on the basis of the datasize of the write data and the pointer information 700A, and the like,and then store the write data in the free space of the extent found bythis search.

According to the second embodiment described above, the write dataregions of the journal logical volumes are divided into a plurality ofextents, and the write data in journals having adjacent (for example,consecutive) update numbers is stored in a distributed fashion indifferent extents. Thereby, it is possible to improve copyingperformance, regardless of the number of journal logical volumesbelonging the same group (in other words, even if there is one journallogical volume in a group). For example, the time during which a storagedevice 150 cannot receive a read (or write) command can effectively beeliminated, and hence the performance of the storage device can beutilized more beneficially. In order to achieve such improvedperformance in a satisfactory manner, it is desirable that the pluralityof journal logical volumes are provided in separate storage devices 150.Furthermore, if each journal logical volume is provided over a pluralityof storage devices 150, then when providing a plurality of journallogical volumes, it is desirable that all or a part of the plurality ofstorage devices 150 providing one journal logical volume do not overlapwith all or a part of the plurality of storage devices 150 providinganother journal logical volume. Furthermore, it is also desirable thatthe plurality of extents are provided in separate storage devices 150.

In the second embodiment described above, after step 1580 in FIG. 15 andbefore receiving a journal read command from the secondary storagesystem 100B, the control sub-system 101A may autonomously implement aread process for the journal that is expected to be transmitted next.Thereby, when the next journal read command is received, in the readprocess in step 1570 there will be an increased possibility that thejournal corresponding to that command will already be situated in thecache memory 130, and therefore the time from receiving the journal readcommand until sending a journal to the secondary storage system 100B inaccordance with that command can be reduced. Here, the “journal that isexpected to be transmitted next” can be taken to mean the journal havingan update number equal to the previously processed update number plusthe number of extents, p, for example. In this case, in the secondarystorage system 100B, the write data in the journal is storedcontinuously in the same sub write region of the same journal logicalvolume.

Furthermore, in the second embodiment, the update information regions ofthe plurality of journal logical volumes (or the one journal logicalvolume) belonging to the same group may be divided respectively into aplurality of sub-regions (extents), in a similar fashion to the writedata regions. In this case, the first and second update informationhaving adjacent update numbers (for example, consecutive update numbers)may be stored in separate sub-regions (extents), similarly to the methodfor storing the write data.

Moreover, in the second embodiment, there is no limit on the number ofextents, p, but in order to issue a read (or write) command to all ofthe journal logical volumes belonging to the same group, desirably, thenumber of extents, p, is equal to or greater than the number of journallogical volumes, n, (in other words, p>=n).

Furthermore, in the second embodiment, it is also possible to implementthe following, as a modification example.

(A) First Modification of Second Embodiment

The control sub-system 101B of the secondary storage system 100B issuesmultiple journal read commands. The control sub-system 101B inserts anextent number into each of the superimposed journal read commands. Thecontrol sub-system 101B carries out the journal read command processingdescribed with reference to FIG. 17, independently, for each extentnumber.

When the control sub-system 101A of the primary storage system 100A hasreceived a journal read command, it implements the journal receptionprocessing described with reference to FIG. 15. In the journal receptionprocess, the control sub-system 101A refers to the pointer information700A, and reads out the update information 310 from the logical addressindicated by particular information elements corresponding to the extentnumber (namely, the retry start address and the read start address)(steps 1570 and 1540).

If the control sub-system 101B of the secondary storage system 100Breceives a journal, then it implements the journal storage processingdescribed with reference to FIG. 18. In this case, the controlsub-system 101B calculates the logical address for storing the updateinformation in the journal, on the basis of the extent number and updatenumber in the received journal and the pointer information 700B, andinvestigates whether or not update information can be stored in thespecified journal logical volume, on the basis of the calculated logicaladdress and the size of the update information (step 1810 in FIG. 18).Furthermore, the control sub-system 101B investigates whether or notwrite data can be stored in the identified journal logical volume, onthe basis of the data size of the write data in the update information,and the pointer information 700B (step 1830 in FIG. 18). The journallogical volume where the update information and the write data arestored is the journal logical volume corresponding to the extent. Atstep 1830 in FIG. 18, the control sub-system 101B may investigatewhether or not write data can be stored in the extent corresponding tothe extent number.

(B) Second Modification of Second Embodiment

The second modification is a further modification of the firstmodification example, wherein the primary storage system 100A acquires aplurality of journals and sends them to the secondary storage system100B, in response to one journal read command. A more concretedescription is given below.

In the journal reception process described with respect to FIG. 15, thecontrol sub-system 101A of the primary storage system 100A acquires andsends the write data stored in consecutive storage regions of the sameextent. More specifically, for example, in FIG. 27, the controlsub-system 101A ascertains from the pointer information 700A, and thelike, that the two write data registered in consecutive regions of thesub write region logical volume #1A correspond respectively to updatenumber 8 and update number 12. Thereby, it generates update informationincluding the update number 8 and a journal containing write datacorresponding to same, and update information including the updatenumber 12 and a journal containing write data corresponding to same, inresponse to one journal read command, and transmits them to thesecondary storage system 100B. After the processing in step 1590 (or1545) in FIG. 15, the control sub-system 101A determines the logicaladdress for storing the two or more update information containedrespectively in the two or more journals that are to be generatedsubsequently. In this case, the logical address is equal to the readstart address plus the value obtained by multiplying the number ofextents, p, by the update information size.

The control sub-system 101B of the secondary storage system 100B havingreceived the journals implements the journal storage processingdescribed with respect to FIG. 18, but in this case, the write data inthe received journal is stored from the newest write data address in theextent corresponding to the extent number appended to the receivedjournal. In the example in FIG. 27, if the control sub-system 101B hasreceived two journals having update number 8 and update number 12, thenit writes the write data in the journal having update number 1 to thejournal logical volume #8, starting from the logical address 700, and itthen stores the write data in the journal having update number 12, in acontinuous fashion following this write data.

Third Embodiment

Next, a third embodiment of one mode of implementing the presentinvention will be described. This third embodiment relates to processingcarried out by the primary storage system 100A in a case where theupdate information or the write data in the journal cannot be stored. Aconcrete description is given below.

In the journal creation processing described with reference to FIG. 13,if the control sub-system 101A in the primary storage system 100A cannotstore the update information or the write data, then copying cannot becontinued in the group relating to that process (1390 in FIG. 13). Inthis case, the control sub-system 101A changes the group status in thegroup information 600A to “suspend”, and implements the followingprocessing. A group status of “suspend” means that the journal creationprocess has been suspended and consistency between the data in theprimary logical volume P and the secondary logical volume S has not beenachieved.

In this third embodiment, the control sub-system 101A providesdifferential information. The differential information is informationindicating whether or not there is a difference between the primarylogical volume and the secondary logical volume, for each storage regionof a prescribed size (for example, for each kB, for each logicaladdress, for each storage volume corresponding to the data volumeprocessed in one initial copy operation, or for a factor or measure ofsame). Differential information is required for all of the primarylogical volumes P. The differential information is stored in aprescribed storage area, for example, a memory which can be consulted bythe channel control section 110 and the DKA 120 (more specifically, ashared memory 140).

(A: Processing implemented when a journal cannot be stored (groupstatus: suspend))

Before the group status of a certain group becomes “suspend”, thecontrol sub-system 101A previously sets the value of the differentialinformation for the primary logical volume P in the group to “nodifferential”. The control sub-system 101A reads out the oldest journalfrom the journal logical volumes in that group, on the basis of thepointer information 700A, and sets the value relating to the oldestjournal in the differential information (for example, the valuecorresponding to the logical address of the oldest journal) to“differential”. The control sub-system 101A then discards the oldestjournal from the journal logical volume. The control sub-system 101Acarries out this process for all of the journals.

(B: Processing implemented when a journal cannot be stored (groupstatus: suspend))

In the processing described above (A: Processing implemented when ajournal cannot be stored (group status suspend)), if the controlsub-system 101A has received a write command and write data from thehost computer 180, then rather than creating a journal for that writedata, it sets the value in the differential information to“differential”. More specifically, for example, the control sub-system101A refers to the group status at step 1265 in FIG. 12, and if thegroup status is “suspend”, then it sets the corresponding logicaladdress (the corresponding location in the differential information) to“differential”, without creating a journal.

(C: Restart of copying after suspension of copying (suspend state)

The control sub-system 101A receives a specified group number and a copyrestart command from the host computer 180 or the maintenance terminal,and in response to this copy restart command, it restarts the copyprocess for the group corresponding to the specified group number. Oneexample of a specific processing sequence is described below. In otherwords, when the processing described above (A: Processing implementedwhen a journal cannot be stored (group status: suspend)) has finished,the control sub-system 101A changes the group status of the groupspecified for copy restart processing to “not copied”. The controlsub-system 100A then implements an initial copy process as described inFIG. 10. In this initial copy process, as illustrated in FIG. 30, afterstep 1020, the control sub-system 101A checks each location of thedifferential information 1021 corresponding to the primary logicalvolume which is the object of the initial copy process (for example, thelocations corresponding to each logical address), to confirm whetherthey indicate “differential” or “no differential” (step 1021). If“differential” is set in the differential information, then the controlsub-system 101A carries out a journal creation process in step 1040, andif “no differential” is set, then it carries out the processing in step1050. When the pair status for all of the primary logical volumes in thedesignated group has become “normal”, as a result of this processing,then the control sub-system 101A returns the group status to “normal”.Thereupon, all of the values set in the differential information arechanged to “no differential”, and normal operation is resumed, in otherwords, a journal is created whenever data is updated.

According to this third embodiment described above, differentialinformation 1021 is used to identify whether or not the write data forwhich a journal is to be created is write data containing a differencebetween the primary logical volume P and the secondary logical volume S,and if the write data contains no such difference, then no journal iscreated. Consequently, journals are not created unnecessarily, and thetime required until the secondary logical volume S coincides with theprimary logical volume P can be shortened.

Embodiment 4

Next, a fourth embodiment of one mode of implementing the presentinvention will be described. This fourth embodiment relates to anexample of a method for setting various information for achieving atleast one of the aforementioned mode of implementation and theaforementioned first to third embodiments. Below, a GUI (graphical userinterface) screen used when this method example is adopted will bedescribed. The GUI screen described below is taken to be a GUI screenprovided by software installed in the SVP 281, and it can be displayedon a variety of computers connected to the SVP 281.

FIG. 31A shows one example of a first GUI screen.

The first GUI screen is a screen for establishing the update informationregion, the write data region and the number of extents, and this screenis provided for each group, for example.

More specifically, for example, in the “Meta/Data Ratio” box, it ispossible to set the ratio of storage capacity between the updateinformation region and the write data region. In the example in FIG.31A, the ratio is set to “16”, which means that if the storage capacityof a journal logical volume is 170 GB, for instance, then the updateinformation region will be 10 GB and the write data region will be 160GB. The values set for particular information elements of the pointerinformation 700A are determined on the basis of the values set on thisscreen.

Moreover, the number of extents can be set in the “Extent” box. In theexample in FIG. 31A, this number is set to “32”, which means that 32extents are established in one or a plurality of write data region(s).

FIG. 31B shows one example of a second GUI screen.

This second GUI screen is a screen on which the user can confirm certainsettings.

More specifically, the group number (for example, “70”) is displayed inthe column corresponding to “JNL Group”, for example.

Information relating to the group status is displayed in the columncorresponding to “Attribute”. More specifically, for example, if thegroup status is “normal”, then the group corresponding to theaforementioned group number (for instance, “70”) is displayed as eithera copy source (Master) or a copy destination (Restore). If the groupstatus is “suspend”, then “Suspend” is displayed, and if initial copyingis in progress, then “Copy” is displayed.

The box “JNL Size (GB)” indicates the total storage capacity of thejournal logical volumes.

The box “JNL Volumes” indicates the number of journal logical volumes.

Furthermore, the journal logical volumes allocated to the group numberare listed, for example, in the display region indicated by thereference number 5001.

FIG. 32A shows one example of a third GUI screen.

The third GUI screen is a screen for acquiring information relating to agroup and making settings relating to a group.

For example, the menu “JNL Volumes” indicated by reference number 5003is selected by the user when a new journal logical volume is to be addedto any group chosen by the user. The user can add a logical volume toform a journal logical volume registered for a group, by selecting anyof the logical volumes from a list indicated by reference number 5005 ona fourth GUI screen illustrated in FIG. 32B, for example.

On the third GUI screen, the menu “Change Option” indicated by thereference number 5004 is selected by the user when the screen in FIG.31A is to be displayed.

Although more detailed description is omitted here, the third GUI screenis also used to investigate unused groups (there the “Attribute” columnis blank). Furthermore, the third GUI screen may also be used when theuser wishes to confirm the group status. Moreover, the third GUI screenis also used when the user carries out operations (issues instructions)in group units, such as starting an initial copy process, or the like.

FIG. 33A shows one example of a fifth GUI screen.

The fifth GUI screen is a screen for specifying logical volumes formingpairs, and confirming the statuses of these pairs.

In the fifth GUI screen, the column “Status” indicates the pair status.An entry of “SMPL” in the column corresponding to this item indicates alogical volume that is not paired, and an entry of “PAIR” indicates alogical volume that is paired and for which data replication has beencarried out normally. If the logical volume is a primary logical volumethen “P” is indicated below and to the left of the icon 5006 and if thelogical volume is a secondary logical volume then “S” is indicated.Furthermore, in the “Status” column, “Suspend” is displayed if the groupstatus is “suspend”, and “Copy” is displayed if initial copying is inprogress.

Furthermore, in the fifth GUI screen, it is possible to create a pairwhen the menu “Paircreate” indicated by reference number 5008 isselected. More specifically, if a primary logical volume is selected,right-clicked, and the menu “Paircreate” is selected in the resultingpop-up window, then a sixth screen such as that shown in FIG. 33B willbe displayed. On this screen, a pair can be created by selecting asecondary logical volume, and a primary/secondary group number, and thelike.

In the foregoing, a preferred mode of implementation and severalembodiments of the present invention were described, but the presentinvention is not limited to this mode of implementation or theseembodiments, and it may of course be modified in various ways withoutdeparting from the essence of the invention.

For example, in the foregoing description, a “number” is used toidentify each element, but it is also possible to use any type of IDcapable of identifying that element, and not just a number. Morespecifically, for example, the ID for identifying a storage system 100is not limited to being a number, and it may also be a WWN (World WideName), iSCSI name, IP address, MAC address, or the like.

Furthermore, a journal may also be stored in the secondary storagesystem 100B by means of the primary storage system 100A sending thejournal and a journal write command to the secondary storage system100B. If a method using journal read commands is adopted, then it ispossible for the secondary storage system 100B to issue commands inaccordance with its own status, such as its load, or the like, and thisimproves convenience to the secondary storage system 100B. If a methodusing journal write commands is adopted, then it is possible for thesecondary primary storage system 100A to issue commands in accordancewith its own status, such as its load, or the like, and this improvesconvenience to the primary storage system 10A.

Moreover, if the control sub-system 101A detects that the updateinformation stored in a journal logical volume of the primary storagesystem 100A has been restored, for example, by means of the secondarystorage system 100B implementing a restore process based on a journalcontaining that update information, or if the journal containing theupdate information has been sent to the secondary storage system 100B,then the control sub-system 101A may discards that update information.The former case can be detected, for example, by means of the controlsub-system 101B of the secondary storage system 100B sending the updatenumber in the journal to the primary storage system 100A, each time arestore process is performed on the basis of a journal.

1. A storage system group, comprising: a first storage system coupled toat least one first host computer and comprising a plurality of firstdisk drives, a first portion of said first disk drives being related toa first logical volume and a second portion of said first disk drivesbeing related to a second logical volume; and a second storage systemcoupled to at least one second host computer and said first storagesystem and comprising a plurality of second disk drives, a first portionof said second disk drives being related to a third logical volume and asecond portion of said second disk drives being related to a fourthlogical volume, wherein said storage system group performs a firstasynchronous remote copy process according to a first status in which:said first logical volume functions as a primary logical volume whichstores data sent from said first host computer, said third logicalvolume functions as a journal storing logical volume in which storesjournal corresponding to journal, corresponding to data sent from thefirst host computer to the first storage system, and said fourth logicalvolume functions as said auxiliary logical volume, which forms a pairrelationship with said primary logical volume and stores datacorresponding to journal stored in said third logical volume, whereinsaid storage system group performs a second asynchronous remote copyprocess according to a second status in which: said fourth logicalvolume functions as a substitute for said primary logical volume, saidsecond logical volume functions as a substitute for said journal storinglogical volume, and said first logical volume functions as a substitutefor said auxiliary logical volume, wherein said storage system group ischanged from said first status to said second status based on one ormore commands, wherein said first host computer, said second hostcomputer or another computer displaying said first logical volume, saidsecond logical volume, said third logical volume and said fourth logicalvolume based on at least one request.
 2. A storage system groupaccording to claim 1, wherein said storage system group receives atleast one command for setting said second logical volume and said thirdlogical volume to said journal storing logical volume groups.
 3. Astorage system group according to claim 1, wherein said storage systemgroup receives at least one command for setting said pair relationshipand for setting said second logical volume and said third logical volumeto said journal storing logical volume groups.
 4. A storage system,comprising: a first storage system coupled to at least one first hostcomputer and comprising a plurality of first disk drives, a firstportion of said first disk drives being related to a first logicalvolume and a second portion of said first disk drives being related to asecond logical volume; and a second storage system coupled to at leastone second host computer and said first storage system and comprising aplurality of second disk drives, a first portion of said second diskdrives being related to a third logical volume and a second portion ofsaid second disk drives being related to a fourth logical volume,wherein said storage system coupled to at least one first host computerand an another storage system and comprising a plurality of first diskdrives, a first portion of said first disk drives being related to afirst logical volume and a second portion of said first disk drivesbeing related to a second logical volume; wherein said another storagesystem coupled to at least one second host computer and said firststorage system and comprising a plurality of second disk drives, a firstportion of said second disk drives being related to a third logicalvolume and a second portion of said second disk drives being related toa fourth logical volume; wherein said storage system and said anotherstorage system perform a first asynchronous remote copy processaccording to a first status in which: said first logical volumefunctions as a primary logical volume which stores data sent from saidfirst host computer, said third logical volume functions as a journalstoring logical volume in which stores journal corresponding to journal,corresponding to data sent from the first host computer to the firststorage system, and said fourth logical volume functions as saidauxiliary logical volume, which forms a pair relationship with saidprimary logical volume and stores data corresponding to journal storedin said third logical volume, wherein said storage system and saidanother storage system perform a second asynchronous remote copy processaccording to a second status in which: said fourth logical volumefunctions as a substitute for said primary logical volume, said secondlogical volume functions as a substitute for said journal storinglogical volume, and said first logical volume functions as a substitutefor said auxiliary logical volume, wherein said storage system and saidanother storage system are changed from said first status to said secondstatus based on one or more commands; wherein said first host computer,said second host computer or another computer displaying said firstlogical volume, said second logical volume, said third logical volumeand said fourth logical volume based on at least one request.
 5. Astorage system according to claim 4, wherein said storage systemreceives at least one command for setting said second logical volume andsaid third logical volume to said journal storing logical volume groups.6. A storage system according to claim 5, wherein said storage systemreceives at least one command for setting said pair relationship and forsetting said second logical volume and said third logical volume to saidjournal storing logical volume groups.